That one is easy: Say thank you with a Mona Lisa-smile, then go on about your day.

It's a pure formalism, because any interpretation of what they said, how they said it, of your own thoughts or feelings on it, is 100% pure speculation. Thus you simply accept it formally with a mild smile and a "thank you" and leave everything else (thinking about it, discussing it, etc.) for a later time.

It's very similar to how you're supposed to take/accept criticism.

on the outside, i just performatively say thanks. or more often deprecate myself.

meanwhile i try to remember the compliment and collect it in my memory with other compliments. gradually, in no hurry, i try to accept that those compliments are given sincerely.

it's worked for me in some specific topics of compliments, like my language ability or certain other skills. I've learned to feel that others sincerely appreciate my contribution in those areas.

but more general compliments or affection from others... I'm still working on accepting.