The reason for wanting to study/work at different institutions is really just so that you see a variety of research approaches. Seeing a variety of organizational approaches doesn't hurt either. But if you study at a place you are in (just a bit) danger of becoming too comfortable. Working with others is a way to break out of that lane.
I question, however, whether working in different countries is all that important, especially if you start out in a large-ish country with a lot of institutions. If you are in Europe, the EU made it possible to do this more easily, of course, as did the general move to English in many places.
But, there are two competing issues.
In the internet age, you can collaborate cross institutions and cross borders much more easily than was possible in the past. Last century if you wanted to collaborate with someone at ETH-Z, for example you either went to Zurich or had to depend on very slow and unreliable mail systems.
The other issue is the pandemic. This has caused a lot of disruption in academia generally and made staying at your doctoral institution for, say, a post-doc much more common as well as much more desirable.
I doubt that, at the moment, staying put will have any negative effects that won't be overcome (even overwhelmed) by good work. So, on your scale, I'd give it (maybe) a 2. In more normal times it would depend more on the actual projects you are involved with. If you aren't stuck in a non-productive situation, then still a 2, but it could escalate if you are. Do good work. Live long and prosper.