Russia has ZERO interests to occupy and annexe Ukraine. Primarily because they know they do not have the economic, political and military wherewithal to make that happen.
Putin and his spokespeople have been stating for years (even before this war) that Russia and Ukraine are one people and should be united into one country. A plan has been leaked from the Kremlin for Russia to absorb Belarus back into Russia by 2030.
The model of world power set up by the US in the aftermath of WW II involved economic domination of other countries, but did not involve physical empire. China has adopted the same model with its Belt and Road initiative. Russia is a different animal, they think in terms of physical empire similar to the way things were in the 19th century.
Russia very much wishes to physically take over and control Ukraine from Moscow.
Russia's primary goals are:
- While Ukraine can maintain its independence economically and politically, make sure it does not become a vassal state to America militarily, which essentially turns the country hostile to Russian interests and has a danger of becoming an existential threat. No different from US interests on Cuba.
- make sure Ukraine does not become a state harboring NATO weapons and missiles aimed at Russia
- make sure they have unfettered land (and drinking water) access to Crimea and Black sea.
- annexing Donbas and other Pro-Russian regions is of strategic interests, but not necessarily a goal - as long as the pro-Russian populace are not forced to migrate or become minorities.
None of these seem outrageous. If the shoe is on the other foot, of Mexico joining the (defunct) Warsaw pact or gets into close military ties with China, you would see America's military would be in Mexico in a heart beat.
Every oblast in Ukraine voted in favor of independence in 1991. Crimea and the Donbas had the most "no" vote, but they still had majority "yes".
1991 Ukrainian independence referendum - Wikipedia
Luhansk and Donesk were still 83% "yes". The overall vote nationwide was 90%. Ukraine wanted to be free of Russia then and they want to be free of Russia now.
Russia has been promoting that the Donbas and Crimea are pro-Russian as an excuse to occupy those regions. After drafting almost every male over the age of 16 who could walk into the army in 2022 and getting them killed, support for Russia in those regions is probably not that huge. The first meat waves the Russians did was draftees from Donbas and Crimea. They switched to prisoners and now just regular Russian draftees because they keep running out ot populations to tap for their meat waves.
When Cuba tried to cozy up more to the USSR and started basing Soviet missiles in Cuba, the US did not invade. Tensions got pretty high, but the regime in Cuba at the time is still there 60 years later.
If Russia tried to put a puppet government in place in Kyiv, it would be overthrown in short order, just as they did in 2014. That's why they want to occupy the entire country. They know a puppet can't stand without the Russian army occupying the country.