I am not sure with using Present Perfect Simplo or Past Simple
***NOT A TEACHER***
(1) I think that if you type "present perfect" and "past" in the search box, you will find many helpful threads.
(2) I agree that it can be difficult to know when to use these forms.
(3) It has to do with time.
(4) Please study these two sentences carefully. They may give you an idea about the difference.
(a) Until noon, it is OK to ask: HAVE you EATEN breakfast yet? (In theory, time for breakfast lasts from early morning up to noon.)
(b) After noon, one should ask: DID you EAT breakfast today? (In theory, time for breakfast has passed. We are now in the time for lunch.)
Thank you for your question. Have a nice day.