For example, editing the question to change Linux Mint 19 to Ubuntu 18.04, or Zorin OS 16 to Ubuntu 20.04, etc.
The way I see it, it depends on whether or not you can know for a fact that the question is applicable to Ubuntu. If you do know it, then an edit that removes the mention of the other OS seems perfectly fine: the site just gained another useful question and potential answers that are applicable to Ubuntu. If you don't know or cannot be sure, then don't edit and just vote to close, that is also fine.
If a Mint user asks a question about
sed, which is in no way different in Mint and Ubuntu, an edit removing the mention of Mint to ensure the question is on topic is just another case of an edit improving a question to make it on topic. Nothing particularly special.
When you see a question posted about a different distribution, you know the question is off topic. So vote to close it! That's absolutely fine. If, however, you happen to know that the question could just as well have been asked by an Ubuntu user, then you may choose to instead edit it and make it on topic. That way, the OP gets an answer, we get a useful question and everyone is happy.
The worst case scenario is that the solution we provide might not work for the OP because they're using a different distribution. That's a shame, but that's why we have a scope. The OP shouldn't have asked here. However, the next Ubuntu user with the same issue will now find a solution here. So, again, great! The OP is only a small (and in many ways the least significant) part of why we answer. The main reason is to collect a repository of useful information and help the millions of users and visitors we have. The OP is just one person.
I have used many different distributions over the years. When I was a Mint user, I would often find my solution in Ubuntu forums. When I was an Ubuntu user, I would often find my solution in the Mint forums, or the Arch forums or wherever else. I haven't used Ubuntu or an Ubuntu-derived distribution for more than 10 years now. And yet, I still find useful solutions in the Ubuntu world.
The simple truth is that questions that are really distro-specific are a tiny subset of the questions posted about Linux. The differences between the distributions are far, far fewer than their similarities. So if you know that a question is applicable to Ubuntu, there is no benefit in closing it, that just deprives us of a useful question.
I guess I am saying that our primary responsibility is to the site. If editing to make a question on topic makes the site richer by a useful question, then by extension, closing said question makes the site poorer and that can't be a good thing.
Now, I am not saying we should go around blindly editing questions and forcing them to be on topic. In fact, I can count the times I felt that was worth doing on my fingers, and without taking off my socks. In most cases, the question isn't really so stellar or the issue isn't so clear-cut, and it's simpler for everyone to just close as off topic. But on those few, rare occasions where a question is really interesting and you know it's applicable to Ubuntu, why not add some useful content to the site if all it takes is a simple edit?
Much of this answer has been reproduced from my answer here: https://meta.askubuntu.com/a/18422/85695.
If a question is about an off-topic distro, it should be closed as off-topic.
We can't assume that a problem or question about Zorin or Mint would exist if the question's author was using Ubuntu.
Furthermore, edits should never deviate from the intentions of the original post. You should never change details, especially critically relevant details like the operating system in use.