Is C#/.NET worth learning in 2022 without being locked in MS ecosystem?

There is a .Net container image, I've used C# for Unity on Linux. Depends on what you use it for. If you are looking for a job, there will be a more narrow market which would likely take you into MS land.

I've made a pretty decent living for the last 20 years being locked into the Microsoft ecosystem. So guess it depends on what your goals are.

you are asking the wrong question

learning to learn is useless and a waste of time by definition

pick a project and commit to it, learn what needs to be learn