It of course varries from one school or area to another, and from different age groups.
I ended up going to 4 proms, my own junior and senior proms, the senior prom my junior year because a girl asked me, and then I ended up dating a girl at another high school after I graduated and ended up going to her senior prom (in case anyone's getting skeeved at that, we were both 18 at the time we started dating, just a few months difference between us, I just barely made the cutoff to be part of the previous grade and she just missed it)
That last prom was the only one where I was actually dating my date, the other 3 we just went as friends, although I did have a pretty big crush on the girl I took to both of my own proms but could never quite work up the nerve to ask her out.
There were never any elaborate promposals or anything, that was just starting around that time and hadn't quite caught on yet, my sister a couple years behind me did it, nothing too elaborate I think she gave her friend a cake and balloons.
The promposal thing is mostly just that it's silly and fun, and nowadays I guess it probably makes for a funny tiktok.
Prom was not a particularly big deal in my area, if I had to attach any particular significance to it, it's just that it's kind of your first "adult" formal event that you're attending for your own sake, not because you're going to a cousins wedding, not something like your first communion or bar mitzvah or whatever when you're still very much a kid. You get to dress up, you get a fancy meal, you rent a limo, maybe you go to a cool post-prom party and you're going to be out till the wee hours of the morning mostly left to your own devices. It's fun for its own sake, and the kind of event most teens don't really get to experience very often.