All of them. Don't be a "stack developer". Be a developer who can build things and get the job done. All of those languages/frameworks are used by 1000s of companies.
The second list only matters once you've checked the correct box. If you go to a .NET shop and say "I've never used Microsoft products before but I'm a quick learner, look at these haskell projects" your resume is going in the bit bucket.
with the exception being if they have some constraint that means you are the only person applying to the job, e.g. they want you onsite 5 days a week in the middle of nowhere and you're the only person willing to move out there
This is actively harmful advice to someone looking for a job. The hiring team is only going to pick one person and if you want to be at the top of that list you need to be familiar with their stack.
_once you have a job_, yes then you can focus on breath and flexibility.
OP's question was whether they should focus on a specific stack to get jobs and they listed all the popular ones. The answer to that is still what I said. That has nothing to do with a company/team preferring to hire someone who knows their tech stack. apples and oranges. Company A uses React/Python etc. Sure, they would prefer hiring someone with experience in that. But then there is Company B that uses PHP/Laravel, Company C that uses .NET and so on and so forth. Plenty of fishes.
