Yes, it is quite open and clear. Among others Prigozhin (before his untimely death) spelled it out.

TL;DR - Putin invaded to improve the stability and security of his regime and to conquer the vast oil and gas wealth below Ukraine’s soil.

Autocracies, such as Putin’s exist because the autocrat enjoys support from critical sections of society, for a better word the “movers and shakers”.

All Autocrats after taking power tend to reassign the positions of power to supporters on the basis of loyalty and not on the basis of competence. This often leads to reduced efficiency in all areas of society.

A “mature” autocracy is characterised in that all available fiefdoms and opportunities for graft and individual enrichment at the expense of the whole society are filled with supporters of the autocrat and there is nothing more to divide and the Autocrat can no longer buy loyalty through assigning such fiefdoms to supporters.

The only option for further enrichment is for either Autocrat unseating one of his supporters (usually waiting for a natural death takes too long) and assigning that supporters former fiefdom to someone else among his supporters or for one of the supporters to actually take it away from another. The result is constant infighting and conflict among the autocrats direct supporters.

This was the case in RuSSia by around 2014.

The main reason for the invasion is that mature kleptocratic autocratic systems are inherently unstable due to the infighting, inefficiency of a country run based on loyalty, not capability, a relatively poor general population with few if any options for advancement and a lack of any new resources or fiefdom’s to buy loyalty through enrichment.

Engaging in military adventures helps stabilise the autocrats rule.

A successful military adventure will give new land and resources to divide and will raise popularity among the general population and may offer additional opportunities for advancement all across the population (e.g. a small time crook may become a police chief in a new conquered territory).

A war will also allow the regime to increase repression of any opposition, creates new opportunities for graft, causes some of the elite to loose their life, opening up options for redistribution of existing fiefdoms.

So even a failed military adventure actually stabilises the regime, compared to the “doing nothing” case.

In Ukraine we have the additional motivation of natural resources.

In 2014 RuSSia’s exports of oil & gas accounted for ~70% of all exports and never fell below 60% and over 50% of RuSSia’s governmental budget came from oil & gas exports.

In 2013/14 Ukrainian society rose up and replaced a pro-russian government that had intended to move Ukraine into closer economic, politic and military integration with RuSSia (similar to Belorussia), in direct contradiction of election promises to seek integration with the EU.

This seriously upset most Ukrainians who seeing both how Polish citizens lived and Russians did most certainly wanted to become more like Poland and less than RuSSia, not the reverse. So the government was replaced (nope, it was not a coup engineered by NATO/USA, that's fake news).

Ukraine has huge oil and gas reserves in the Donbass and around Crimea, that have not been tapped at all:

Agreements had been signed between Ukraine and western Oil & Gas companies to start exploiting these reserves and to start production.

These fields would have offered a price advantage over RuSSia’s older fields, both a result of more favourable weather, geography and mor modern methods.

Most of the Soviet Era pipelines for oil and gas into Europe pass though Ukraine and these sections being owned by Ukraine which charges transit fees.

Thus Ukraine not only had Oil & Gas resources easier and cheaper to produce output from compared to RuSSia but also a ready made transport infrastructure with eager existing European customers on the other end.

A Ukraine in the EU would have given the EU energy independence from RuSSia and would have brought huge wealth to Ukraine, which would have boosted the living standards of Ukrainians way faster and higher than for example Poland experiences.

This would happen even with the existing corruption in Ukraine continuing, which membership in the EU would likely strongly mitigate against.

Thus RuSSia stood to loose significant market share of it’s main exports to Ukraine, which would have caused incomes for the elite and the government to fall dramatically. Of coure, as consequence of the war it lost this market anyway.

On top, Russia would have had a prosperous democratic Ukraine just across the border (not in Germany, France or UK). Somewhere where many RuSSians have family ties.

It would have easily been compared with the very limited prosperity and even poverty in RuSSia caused by all pervasive kleptocracy, despite huge natural resources in RuSSia. The impact of such a “shop window” to the west and it’s systems cannot be underestimated.

Thus a EU aligned Ukraine with functioning oil and gas fields would have been by it’s very existence a huge factor undermining the autocratic kleptocracy that made Putin and his supporters incredibly rich.

By invading Crime and annexing it 2014 and by creating RuSSian backed and RuSSian intelligence services led terrorist groups in Donbass (the so-called Separatists) Putin in effect blocked the Ukraine’s path into the EU and NATO and caused western companies to exit any oil & gas deals.

It also destabilised the Ukrainian government, made democratic and anti-corruption reforms needed to join the EU difficult as the country was de-facto at war.

In doing so, RuSSia broke many agreements and treaties.

Crimeas annexation boosted Putin’s popularity. While not a lot of extra opportunities for graft existed there, for a while expanding into Crimea gave small additional opportunities of enrichment and stabilised Putin’s regime for a time.

And the ongoing hybrid war in Donbass large froze the situation in Ukraine, which did not serve Ukraine and Ukrainians but was favourable for RuSSia. Over time RuSSia sabotaged all attempts to resolve the issues in the Ukrainian East, keeping Ukraine from being able to move forward joining the EU and possibly NATO.

While sanctioned by the west, the sanctions were not very serious and RuSSia continued as usual and also started to intervene in Syria, where the limited RuSSian contingents committed extensive war crimes including using chemical weapons against civilians, however they were mostly sucesfull, convincing Putin his military was actually competent and capable.

By 2020 the situation in RuSSia was again at no further enrichment or new opportunities and Covid had actually impacted not just common RuSSian citizens but also the elite negatively. Again, unrest was growing and Putin could see his power slowly slipping.

Putin’s solution? Conquer Ukraine completely. As Prigozhin outlined, make his buddy Viktor Medvedchuk Ukrainian president, turn Ukraine into another Belorussia and divide the Ukrainian economy among his supporters.

And Putin somehow expected the world and especially the EU and USA would just stand aside and let him do as he pleased.

Of course, following success in Ukraine, it would not stop in Ukraine. After Ukraine fell in less than a week (or so Putin thought) and West did nothing (or so Putin thought) that would be in any way be effective against RuSSia, the Baltic Republics could have been next and Poland was on the list, as well as Moldova and possibly Romania.

Alas, his army utterly failed to even subdue Ukraine and has been bogged down with 18 Month (update - now almost 36 Month) of War RuSSia is loosing.

RuSSia is under an unprecedented level sanctions and is facing slow but certain economic ruin.

Far from what Putin wanted and expected.

HOWEVER it STILL stabilises his regime, as long as the war continues. Law's passed to suppress dissent have increased hugely since the start of the all out invasion and expressing dissent openly in many cases carries longer and harsher sentences than rape and murder!

So it's not all bad news for Putin, the war continues and he continues as president.

If we take a longer view from the European and perhaps worldwide perspective, RuSSia under Putin operate

s on the White Slavic Supremacist and Fascist Ideology known as “Russkii Mir”, a clever word game as Mir means both world and Peace. So RuSSkii Mir is the RuSSian Peace that will descend upon a RuSSian World, when RuSSia rules all of it, certainly all of Eurasia (including India and China) and like Arabia and Africa too.

Russian World. Have you heard about it?

One thing is made very clear by both Mr. Putin’s motives and by the actions of RuSSia.

If there is to be lasting peace in Europe it is absolutely necessary to extinguish RuSSia as geopolitical, socioeconomic and probably ethnolinguistic entity.

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