Putin was popular in Russia in 2022 and his domestic enemies were weak. Putin didn't need a war to hold on to power. Wars are sometimes fought to distract from domestic problems, but that wasn't the case here. Putin has argued for more than 20 years that the Russia/Ukraine border was not determined correctly when the USSR fell and that the 1991 borders were "unfair" to Russia. Add to that Ukraine's cultural shift away from Russia, messy elections, NATO, and the belief that Russia would easily defeat Ukraine and it's pretty clear why Putin decided to invade in 2022. No reason to hypothesize alternative theories. Putin is still very popular especially among older generations despite the heavy cost of the war.