You're asking questions we have answers to and you seem to have totally missed some key facts.
Ukraine is under martial law and has been since the invasion. There are no elections, they've been cancelled due to the needs of the state. There is no concern of the government being replaced.
Ukraine isn't a proper democracy but a "hybrid", e.g an oligarchy anyways. The popularity or unpopularity of policies doesn't translate into political outcomes so easily or transparently.
But your argument about authiritarian regimes is faulty. We just saw the complete opposite of that in Syria. Authoritarian regimes do not necessarily command loyalty and they also live in constant fear of popular unrest or dissatisfaction. In fact, there are many analysts who point to Putin's current domestic policy choices as desparate attempts to placate the Russians that have lost something due to the war.