Kindly, if you have time, figure it out by yourself. Below I explain some stuff that might help you to draw your own conclusion.
By the way, I'm a gold tag badge holder here and in Stack Overflow, but I haven't many answers in Super User yet.
A certain overlap across Stack Exchange sites is normal as the definition is at a broader level, not something so specific as Google Sheets formulas.
It's possible to find questions about Google Sheets formulas in (in descending order of the site age):
- Stack Overflow
- Super User
- Web Applications
There might be other sites. You could try the global search in https://stackexchange.com.
Regarding our main site
Most of the users that answer questions about Google Sheets including Google Sheets formulas also answer questions about Google Sheets formulas in Stack Overflow and Super User. You could confirm this by looking at the Top Users page of google-sheets.
As of April 29, 2023, google-sheets is the Web Applications top tag by popularity (determined by the number of questions).
Web Applications is a site about using web applications by end-users. Besides formulas questions about other Google Sheets features, when they are used from an end-user point of view, are allowed.
Regarding tags
Please bear in mind that having tags with the same name in multiple Stack Exchange sites doesn't mean that the tag usage is exactly the same. Each site has its own workings. Some sites might put more attention to the tag wiki than others so the best is to study each site than rely on the tag wiki.
About other SE sites
Stack Overflow is a site for programming questions. In their per-site-meta there are discussions about if spreadsheet formulas are on topic or not. As of April 29, 2023 questions about Google Sheets are allowed and have several users actively answering questions.
Super User is a site for questions about computer software and hardware with certain limitations. Questions about web applications are off-topic, actually, it's fair to say that Web Applications Stack Exchange is a Super User "spin-off" as it was proposed by a Super User moderator at that time and most of the committers to not say that all of them were active Super User users. Questions about Google Sheets formulas are "tolerated" when those questions are about features supported on installable spreadsheets apps like Excel.
Note
A bit later I will add links to related posts.