There have been suggestions that Crimea’s dependence on gas and electricity from the mainland makes it uniquely vulnerable to a Ukrainian blockade.
Well, no. It does not. The Russian military presence itself does not depend on imported anything from Ukraine.
The civilian population does depend on imports from over the border, but inflicting hardship on them would be guaranteed to increase support for Russia by a multiple. Morale in Crimea (and the Russian Federation) would go through the roof. Wartime conditions have that effect on people.
Meanwhile the Russians would be shipping in supplies to keep the Crimeans from freezing or starving, at some cost but a bearable one ... and any Ukrainian attack on those shipments would provide a perfect casus belli and deprive Kiev of the moral high ground internationally.
Consider the evidence in Bombing to Win, by Robert Pape of the University of Chicago. Strategic bombing universally failed to demoralize populations. Why would a strategic blockade succeed?
If you doubt that, consider what happened in 1948. When the Soviets blockaded Berlin, the Berliners were not demoralized and the Western Allies did not roll over. Nor did the Soviets attack the supply aircraft, despite being in a much better position to do so than the Ukrainians would be today.
An attempt to blockade Crimea would be 1948 in reverse. It would be stupid. All indications are that the people in Kiev realize that. That is why (I hope!) it will not happen.