Odessa is a Russian city, created/established by Russians, and still too many Russians living there to allow it top be ruled by Kiev. Russians can govern other people and allow them to live decently; hohos can’t.
By that reckoning Vyborg should be returned by Russia to Finland, Koningsburg / Kaliningrad should be returned to Germany, Vladivostok to China etc.
Odessa was founded in the Tsardom of Russia. That state ended in 1917. The USSR explicitly said it was not a successor state of the Tsardom, and modern day Russia says it is a successor state to the Russian Soviet federation and not to the Tsardom.
Odessa is a Ukrainian city de facto and de jure since 1922.
The majority of people living there do not want to be part of Putin’s Russia.