MS stack will be high quality and used by clients with $$$ for the rest of your career.
With that said, any serious non-MS shop will be happy to have your experience and so switching up stacks shouldn't be a problem either if you find a good team.
I would just apply broadly and go from there.
I imagine in two or three hundred years though we will have moved past COBOL completely. That being said the idea of some future advanced civilization trying to wake up some old programmer from cryo sleep so they can decipher an ancient mainframe that is still somehow running does make me laugh!
I've yet to experience a MS product that I would consider to be "high quality" (including Azure)
Most aren't. Some are. As with all software/ecosystem providers.
random incomprehensible error messages, near constant UI timeouts and terrible UI performance and experience (artifact deployment has been "skipped"? why? no way to know), etc
the Windows VMs are also extremely slow compared to my employer's non-azure VM, with the Azure VMs having double the VCPUs, disk IOPS and RAM (despite having the same "stack" deployed on it)
The VM speed I can't comment on.
As someone who has used the MS stack, I have yet to witness anything I would call high quality.
It has regular improvements and is LEAGES more well-design than JavaScript and I'd say Java.
Sure, it's no GO, but it is ever evolving.
Blazr is relatively new compared to Microsoft's other libs but I'm sure in 5-10 years, it will be solid. It took .net core years before it became decent.