I would say, "not as such". It is easy to imagine some support questions ("How do I reset my password?") which are obviously not TeX-related. But a user, especially an inexperienced one, will often have little idea about the source of their problem. They may (wrongly) think they have a TeX problem, when they don't; and they may also wrongly think they have a frontend-related problem, when they don't. We often see questions which are obviously pure TeX issues where the user tells us that they are using MikTeX, or a particular editor, or whatever.
Unless one is a rigid purist, questions about how to compile, or where to place files, and the like are capable of being on-topic. This issue, as moewe notes in this comment is really not different from questions about any editor or compilation system. That doesn't mean that any and every overleaf-related question is on-topic, just that we don't need any sort of "special rule" here.
In practical terms, TeX and LaTeX are not just single executables, but (for all of us) a complex ecosystem of programs which all have to operate together if one is going to get any useful work done. Although some parts of the toolchain are more interesting, this site proclaims itself to be concerned with the system not just the program. Although I suspect overleaf questions will often be rather dull "one-off" ones, I don't think they deserve any special treatment.
Pragmatically: the extent to which new and inexperienced users receive (within reason!) patient answers to questions, asked in good faith, which an experienced user regards as pointless, obvious, or based on a fundamental misunderstanding is a fair measure of the extent to which a community will be regarded as welcoming. Policing boundaries over-relentlessly, especially when they are boundaries that aren't obvious to the person asking the question is nearly always a mistake. That commits nobody to answer anything. Although I'm sure it isn't the intention, a "rule" that "overleaf support questions are not on-topic" would send the wrong message.
I'd always rather a person said "When I started using TeX, I had a really dumb question because I just didn't understand how the system works, but I got it answered, and now I'm about to finish my dissertation" than "I tried using TeX, but I just couldn't get it to work, so I went back to Word."
