The state is functional in non occupied territories, so organising elections, something that have tried and tested procedures should be doable pretty easily. If anything, single look at previous elections map means that, even without banning opposition, territories most supportive for the government and Ukraine are still in and separatists and opposition are out, so it should be a landslide victory (especially that opposition is banned).

lincoln managed to hold and win an election while half the US was under control of slavers.

the slavers of course did not hold elections.

hmm hmm. all this in the 19th century, with 19th century logistics.

anyway, ukraine cant hold elections clearly.

That seems like a pretty weak excuse for cancelling the election, especially given that it would effectively be a referendum on whether to continue the war or not.