The interesting thing is that Russia already has two ice free ports on the Western side of the country: Kaliningrad in the Baltics and Novorossisk in the Black Sea, just East of the Crimean peninsula. There's no real need for another port in Sevastopol. And on the Pacific they've got Vladivostok and much of the Kamchatka peninsula.
Sevastopol helps them keep firm presence on the Black Sea and from that the Mediterranean so long as Turkey allows them through the Bosporus and Dardanelles to the Aegean. They don’t want their presence being dependent on Crimea’s holding
Too bad they messed that up by invading Ukraine. Russia had a lease on Sevastopol up through 2042, now they'll be lucky to keep it for the next 5 years.
Regardless, Baltic Sea access isn't super great when you're entirely choked out by Denmark for access to the Atlantic. Same goes for Black Sea and access to the open seas - Turkey and arguably also Spain/UK block several times on the way.
The Pacific ones freeze over and are kind of blocked by Japan, essentially.
It's going to be interesting to see how much Russia's geopolitical position improves from rising global temperatures - if their pacific ports become ice-free, then that changes the game quite a bit.
Kaliningrad is an exclave and not connected to the rest of Russia. Good relations with Poland, Lithuania, and Belarus is the only thing thay allows goods to pass through Kaliningrad. Sevastopol is a superior port to Novorossisk for many reasons, but the biggest one is the crntral location in the Black Sea. The Black Sea Fleet can quickly deploy anywhere in the Black Sea from Sevastopol.
Vladivostok and the Kamchatka usually get iced in during the winter as arctic sea ice moves way down to the Japanese islands. Obviously that is becoming less and less of an issue, but that's why Russia claims the Kuril islands.
There is a vast untapped natural gas field southwest of sevastopol. On top of giving Russia another warm water port, it also gives them rights over the slarwa of the black sea where the gas field is. the argument has been made that this was the reasoning behind the Crimean annexation in 2014.