"What is all this crazy blaming paint for issues outside it’s sphere?"

Because sometimes it actually IS the paint. I had a powder room in my other house painted a very similar deep color to the OP's bathroom; it might have actually been a bit darker. I chose a flat finish, and IDK what the heck was with that paint but I told DH don't touch the walls!! every flippin' place the wall was touched left a chalky mark. Maybe I got a bum batch or something, but it was definitely the paint.

ETA: OP -- to get good suggestions, take a couple more pics showing the shower and the flooring.

The room is lovely. Yes, my first thought is that the more sheen in the paint, the more you will notice moisture. Do your teens even run the fan after their shower? I have a small bathroom with a fan installed in a very high ceiling. I have to run the fan for quite a while after even a short shower.

If you don't think ventilation is the issue and you do repaint, I recommend BM Aura Bath. I used this in Sapphire Ice 808 in my son's bathroom in our previous house. I have Breath of Fresh Air 806 in my powder room now. Those are both nice blues. I cut Breath of Fresh Air 50% and it's still quite blue. Both 806 and 808 are lighter than what you currently have, and 807 is in the middle if that's what you want.

The color is beautiful. I have an eggshell finish on pumpkin colored walls and you can still see the water at certain angles but not so much. The exhaust fan will certainly help. Up grade to a model with a humidity sensor or a timer switch. It should be left running for 20 min or so after a shower.

A lighter color may help hide the water marks but they are still there.

Good luck!

A contractor I know says to put the fan on a timer and set it for 60 minutes. And also to keep the door closed during that hour.

Totally not your question, I know. What is the wall colour outside of the bathroom?

It's a beautiful color. Hopefully a different sheen will be the fix. I don't know paint colors like others on this forum. If it is a ventilation issue maybe a dehumidifier can be a short term solution until the venting issue is fixed. Or if your kids aren't even turning the fan on, one fix is to put that on a Z wave or smart switch. That way you can control it.
You also asked about the side-by-side windows. Adding curtains might be awkward given the vanity and the one towel bar. Roman shades would be nice but you've just installed the new blinds so maybe just leave as is.

I find when you have condenstaion on the walls it is a lack of venting , we foud opening a window along with the fan worked to aid with venting. I nice satin finish on the walls also helps , For me the walls ar really dark so maybe the same colors just lighter shade , I think the windows are fine as they are . Th fact is you have no real protecttion from the mosture with that style of shower and shower curtain so the ventilation needs to really be good .Yes to atimer for the fan and we let ours run for 1 hr.The lighting needs an upgrade too I like hooks for towels but that is becasue no one in my house folds a towel neatly for a bar.