And what's your gender?
I've seen this painted as a gender-specific thing or "sexism" (and all this stuff about the "male gaze"), but not seen any evidence of it. Seems like one of those normal life situations that's painted as happening to one gender more than the other, without that being the case, and it becoming a popular narrative – the Google AI sources seem to literally be reddit threads from gender-specific subs, and no controlled studies.
I'd say since childhood and deep into my 20s I got told to "smile!", "cheer up", "it might never happen", "you never smile do you", "you have a nice smile, you should smile more often" mostly by older women but also by other men, and quite frequently for most of my life, until I mastered being able to fake smile/generally putting myself into a happy mood while around people. Can't say I ever considered it sexism, just as annoying and having the opposite effect of its intent. I have a male friend who has a similar experience, except for the learning to look happier part.
Same goes for the older female colleague who looked visibly annoyed when I didn't laugh at her joke when I happened to hear it (not even directed at me) and for weeks after that began spreading random rumours about me being lazy (which luckily nobody believed, since I'd already got a reputation for doing lots of work). Again though, I wouldn't call it sexism – just someone being a stuckup prick.