Ukraine's plans to reconquer Crimea militarily may be impossible or unwise.

The places that Russaian troops were stationed since 2014 include, as a fact, parts of the Donetsk and Luhansk regions, but Putin always denied that this was the case. He should not be invited to acknowledge it belatedly now and reap any benefit.

To negotiate the fate of Crimea is more sensible. An honest election would have been a legitimate approach in 2014, but Putin drove out or exiled those who supported Ukraine, then (according to this article) lost anyway and lied about the result.

Putin's elections in Russia are blatantly dishonest.

The population of Crimea today is different from the population in 2014. If an election is to be held now about which country Crimea should belong to, which people should vote in it? To give the decision to the current population would mean that Putin (or anyone else) can conquer territory and legitimize that with an unfair election. To give the decision to the 2014 population might be asking for further violence.