Ukraine continues to defend their rights to this peninsula.
What kind of "rights"?
Crimea was autonomous entity
before USSR was formed, and Guirey's (dynasty of Khans) descendant was one of the signatories
in the Soyuzny dogovor (Treaty of Union) of USSR.
It's population consisted of Russian majority and of Tatars, the previous invaders, now a minority.
After WWII, Stalin expelled Tatars and downgraded Crimea to just an "oblast" which was rolled back in 1991 by people of Crimea,
they restored their autonomy.
Ukrain is Unitary State by it's consitution:
https://en.wikipedia.org/wiki/Unitary_stateany administrative divisions (sub-national units) exercise only the powers that the central government chooses to delegate
Whereas the original Crimean Constitution of 1991 stated that Crimea is a sovereign state, voluntarily ceding certain powers to government of Ukraine.
So in fact, Ukraine + Crimea was a confederation (if not even looser kind of Union of two States).
This Union broke down in 2014 after illegal coup d'etat in Kiev.
What kind of "rights" can confederation center have to any regions, if those regions stopped ceding their sovereign powers by referendum?
Sevastopol, as distinct of Crimea, was never a part of Ukrainian Soviet Republic. It was directly subordinated to USSR, as it was home of Soviet Fleet.
Sevastopol was "gifted" by Yeltsin who shot at Russian Parliament from tanks (after Parliament made a decision to take Sevastopol into Russian Federation).
These are hard historical facts. You can mock them all you like, speak of Dinosaurs and cetera, try to manipulate weak minds all over the world with "fredom vs slavery" propaganda, but they remain as they are regardless.
Nikita Khruschev and Boris Yeltsin traitorously stole and sold Crimea and Sevastopol from Russia, each of these traitors gaining his own benefits for that act. Years 1991-2014 were illegal occupation of Crimea and Sevastopol by a new state of Ukraine, who is not even a de-jure successor of Ukrainian Soviet Republic. They didn't pay USSR sovereign debt and they denounced Soyuzny Dogovor (Treaty of Union) losing all claims to about a half of it's territory, ceded by that Treaty.
If you doubt this conclusion, consider the fact that annual rent for Sevastopol (to which Ukraine had absolutely no claim whatsoever) was 3-4 billions USD. And you think Yeltsin's "family" didn't receive any kickback?