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.
_once you have a job_, yes then you can focus on breath and flexibility.