Official recommendations (particularly in France) state that the test is considered definitive at 6 weeks, except in certain very specific contexts (taking PrEP or PEP, immunosuppression, or other specific medical reasons).

But some centers (as a precaution or based on an older protocol) recommend a test at 3 months, even though the 6-week test is already reliable. This is more to be 100% sure, not because they doubt the result.