I may not be able to refactor the system to use micro services or whatnot, but to dig into the code and start fixing some bugs or even add a small feature has always been a week 1 goal for me (and one I set to the people I manage now).
If you have a less popular tech stack then you need to be more flexible. You aren't going to get a lot of developers that know everything and you will need to look at how adaptable they are.
Where I work we don't particularly care about specific experience with our stack. A good developer is a good developer regardless of the stack. And we set aside time for people to get comfortable with the code base. It's not expected that even seniors come in and make contributions on day one. Obviously it's more generous to juniors and mid level developers.
That's why I said list what's relevant to the job, but don't list your entire life story there. If you're an expert that can hit the ground running, then make it known. But if you're applying for a front end React role and you're listing PHP experience from 5 years ago, it's probably not relevant. You can use that space to detail more about what you're good at.
From my experience, at least in Europe, companies are paying the most for people who can "hit the ground running", i.e. being able to contribute from day one - both in terms of code as well design/architecture decisions. That neccesitates knowing their exact tech stack.