I say this as someone who loathes .net: learning .net is a really good idea. If you're looking purely at making a decision based on the labour market, I doubt you'll find a bigger demand relative to supply, and among typically well funded and stable companies.
I’ve been doing .NET since 02 and very happy with the language and ecosystem and job opportunities. However nowadays a lot happens in JS land but with Typescript I enjoy programming there too. .Net + Typescript is a great combo.
I dont neccesarily discount it, but I dont have any .net core or Azure experience significantly and it seems any half decent job is using those. Also I'm kinda sick of windows, but thats not something overly important job wise