I would treat Azure as a separate topic, compared with AWS is coming strong from behind.
As for the .NET stack, you have to be more specific, what is your career path? In what industries you want to work? What kind of projects? How many jobs there are in your area?
Because you didn't specified any of these, I will answer from a statistics point of view, No.
Less popularity means less jobs available, less career opportunities, less projects to handle and so on.
If you want to be more specific, like in banking industry, we may have other answer. Except for VB.net and ASP.net, I will say no regardless.
"Less popularity means less jobs available, less career opportunities, less projects to handle and so on."
What you're not mentioning here is that "less" isn't necessarily a problem. "Less" than a helluva lot is still a lot. I've been working as a C# .NET developer for a whopping 7 months, and my LinkedIn inbox gets about 3 or 4 unsolicited messages per month from people looking to hire. This has been going since my second week on the job.
Might there be less C# jobs than JAVA jobs in the market? Sure. Will you struggle to find work as a C# developer? I seriously doubt it.
Sure, but in a small city, less could means there are only 3 jobs compared with 30 in Java, and that could be a struggle.
Less in a small industry could be the same.
Anyway, learning a strong type language like C# is a strong addition in any developer arsenal.
I think different stacks have different popularity by region. Here in Stockholm (and Sweden in general) nearly every job listing is for either a JS full stack type position or C#/.NET. Java is way less popular here. So OP should definitely check their local listings first.
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