The community is centered on people with experience or interest in using or administrating the (GNU/)Linux operating system on servers or desktop (including laptops, excluding most phones and tablets) computers.
Topicality of questions
This community explicitly doesn't attempt to place itself within a taxonomy of question topics. Any question is on topic if the intended audience is people with experience using Linux. Any question is off topic if the intended audience is a different set of people.
Yeah, look. Sometimes someone is going to be running LibreOffice on Linux and there's going to be a bug that causes their page to look corrupted when they use a certain function. They haven't been able to figure out any more than that from their own research, so they go to their Linux User Group and someone there has seen the same thing, caused by a particular version of a graphics driver. It doesn't matter that LibreOffice can run on other OSes, and it doesn't matter that the person with the problem didn't and couldn't know whether the problem was caused by a LibreOffice issue or a Linux issue. What matters is that the person with the problem connects with the community containing the people most likely to have relevant experience. This is the community of people with Linux experience—think of it as an online LUG in Q&A format.
So what about macOS, BSDs, and other Unix-likes? What about Android, WSL, Linux on embedded devices, and other Linux deployments beyond traditional server and desktop?
People are welcome to ask questions on those topics here as long as those questions are directed at the community centered in the first sentence. They should have a good sense of why this community's experience might be relevant to their question before they post.
But why so narrow? Why not just target a broader scope in the first place?
Because experience with Linux on the desktop doesn't equate to experience with FreeBSD or experience with WSL. The goal of this specific scope proposal is to rally people with an area of common experience, not people with different experiences that are technically related to each other by a kernel or a POSIX standard. People with common experience will have interesting things to ask of/say to each other, will be able to reach consensus via voting, etc.
If it turns out that of the people here with Linux desktop experience, most of them also happen to have (e.g.) BSD experience as well, then it would make sense to me to choose a scope that explicitly centers BSD as well. I don't expect that will be the case but I will withdraw this proposal if I'm wrong.
Overlap with Software Development
To reiterate, any question is on topic if the intended audience is people with Linux experience. So, a question about developing software either on or for Linux would likely be on topic for both the Software Development and Linux Codidacts. A question about implementing a FUSE filesystem, even if the asker is developing on and for a Mac, could also be on topic here—the asker doesn't have to be a Linux user, and the topic doesn't have to be Linux-exclusive. The one and only criterion is whether the asker wants the input of people who are experienced with Linux on the server or desktop; ideally, the question will be written in such a way that it is clear why the asker wants said input, as opposed to the input of a broader community of software developers (or any other Codidact community).
There have to be some off-topic topics though
Only if the asker didn't read the sign above the door. A question asking about how to clean an oven is probably off topic. A question about how to uninstall an app from an iPhone is probably off topic. (I say ‘probably’ because those questions could in fact be on topic if and only if the asker has a good reason to ask the Linux community specifically about those things—I can't think of one, but that doesn't mean one can't exist.)
It should be clear, either from the topic of the question or from context written into the question, what the connection to the Linux community is, and if that's missing, we will politely ask you to add it or retract the question. But as long as it's there, any topic is fair game, as long as the question isn't bad for other reasons (too broad, too subjective, didn't try to solve before asking, etc.).