I have an SQL schema and I have some doubts whether the schema is going to massively change in the future. The schema describes entities of a game like user, rooms, board etc.
Would a question concerning the above be on topic?
On topic - probably yes. But you have to be careful to keep it focussed enough, so it won't get closed with the standard "needs more focus" closing reason. This depends - obviously - on the specific question you are going to ask (and also on the moot of certain community members here, who often close-vote for reasons I don't understand).
I can tell you how I would vote:
If a questions just puts a scetch of the schema here and then ask for a general review, with the unspecific goal of avoiding changes in the future, I would probably vote to close it as "not focussed enough",
if a question asks about one painpoint in the schema, presents which alternatives the askers see, what they tried and why it still did not suit their needs, then I would usually not cast a close vote (and if I can, try to answer the question)