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.
I agree with everyone saying that you shouldn't worry about the "best" stack and just worry about being a good developer. But that just raises the question: how do you become a good developer and start getting job offers?
Obviously, there is no easy path. But here is what helped me:
The most important thing is that you HAVE to work with other good developers. Software engineering is only partly about explicit book knowledge. You can't just learn it by studying or even building on your own. You have to build complex software in a team in order to develop your instincts and judgement. And, of course, the easiest way to get a job is to be hired by someone who's worked with you before.
I know this sounds like Catch-22: you can't get a job unless you first get a job. In reality, this is just recursive. It's just like bootstrapping. Start by getting any job you can and learn from it. You'll build up more skills and more contacts to be able to get another, better job (maybe at the same company, maybe at a different one).
If you already have a software engineering job, then you need to maximize what you get out of it. No matter what stack you are using, you need to become an expert at it. And if there is someone who is better than you, learn from them.
If not, then it's probably time to leave. Ping you contacts, do some research, and pick some companies that you'd like to work at--preferably ones that (a) have strong developers you can learn from, and (b) have problems that you can actually solve (e.g., are using stacks that you're good at).
But if you don't have a job yet, you need to start somewhere. Build up a list of companies and job openings and start applying to them. Keep track of the requirements and skills and apply to the ones that are the best fit. Don't worry if you don't have all the skills they ask for. As long as you have a reasonable subset, apply.
Next, track the responses. Most of the companies will ignore you, but some might do a phone screen. If so, then track the ones that do. Is there a pattern? Maybe all the companies asking for Python skills ghosted you, but the C++ ones reached out. If you can spot a pattern, try to exploit it. Apply to companies with similar requirements and see if they are more likely to respond. Or update your resume (maybe by learning new skills) to see if you can get a wider set of responses.
None of this is easy, unfortunately, but it will be worth it in the end. Good luck!
It 2020 being a warm body was enough to get you a job. But in this market there will be a dozen people with directly applicable experience applying as well, those people will get the first calls back.
I've definitely never seen a company prefer a candidate with zero experience in their stack over someone with experience. Slack is given to juniors and people who are adjacent to the desired stack plus have other desired skills, but if you apply to a completely alien stack, i can see your search taking a very long term. I think the only exception I've seen to this is a company that was doing microservices before it was a particularly common skill, so they'd take anyone who could prove they understood the concepts. Even still, most people they hired had an overlap with the desired stack. I just can't see a company with a common stack and a common architecture prefer to hire candidates outside of that stack.
Look at job listings and use AI to map each listing to a tech stack and then do some arithmetic to group similar stacks. I can do this for $80B and a legal training set.
It's better to work on AGI because it will solve all those fields as a corollary to its main function of being a self-perpetuating technological system. Any such system will need the listed functions especially if it operates on a planetary scale.
