I am a middle aged woman who went to university where I studied French. This was 30 years ago . If someone asks me: "what have you studied?" can I answer: "I have studied French at university"(without mentioning when), because this is an achievement and/or life experience or is past simple a better option because the studying happened thirty years ago? Or are both possible for the reasons given?
If someone asks "What have you studied?", it would be fine to say "I've studied French". This makes a connection to the present: You imply "And so now I understand French literature..."
When you add "at university", and especially if you add "30 years ago", you are shifting the time to the past, and it would be very natural to shift to the past tense (especially as 30 years is a long time - tell me about it)
So it would be natural to reply.
I studied French at university.
This doesn't make the present perfect wrong, and you can use it if you want to make that connection to the present, perhaps as one of a sequence of things:
I've studied Maths and Literature at Lyceé, French at university, Education as a teacher and accounting, which I took a correspondence course in, last year.
(note the shift to past tense as soon as a specific time is mentioned)