You say the first paragraph is if I don't agree with the idea that you shouldn't have sex with people who are considerably dumber than you. It's generally a little icky if you have sex with someone who is mentally deficient.
You can't really solve the problem of isekai protagonist not being able to have sex. But when you can't have sex, it doesn't give free license to have sex with children.
Plex is better at looking up show names, has an easier UI to set up more complicated stuff like hardware acceleration, has better clients across a variety of platforms... the only reason I'm using Jellyfin over Plex at this point is because I anticipate Plex shitting the bed. If you're on Plex, there's no reason to swap from it, and honestly if you're comparing the two as a newbie, Plex is still a much easier option.