Taiwan is a completely different kettle of fish.
Firstly - it’s an island. That’s going to make invasion far, far more difficult than invading the flat land next to you
Secondly - the south-east of Ukraine is somewhat in the flux between Russia and Ukraine - a sprachbund. The allegiances are mixed. Mostly it is “jesteśmy tutajsi” in response to what nationality i.e. “we are from here only”
Thirdly - the Russians are battle hardened. The last war China faced was 60 years ago.
Even if the US doesn’t do anything for Taiwan, China will lose thousands or more troops. And in modern China that’s not going to fly
I repeat, Xi is going to move on Taiwan soon.