12 YO boy, I think an introvert but also worryingly narrow interests - any experience?

[DolorestheNewt]

Sorry for long message title, but it seems to be helpful to describe the post in the title!
I have a 12YO boy who will start Y8 in September. Anyone else got one who hates being on holiday and just wants to be back home? He's an only child, so we took him somewhere with kids clubs last year, and he didn't want to go, saying he wanted to hang out with us. So this year we didn't try to repeat that, and came to a hotel with a pool and a nearby beach, but he has been crying, saying he knows he is ruining our holiday but he hates being away from home.

One of my DDs is generally not very good at certain things (well, she is academically able but is at an academically selective school where everyone else is bright too). The other children all seem to have another string to their bow (or serious hobby), like drama, art, sport, music etc, and she does not. She is shy and has a quiet voice, so although she enjoys drama she does not have enough stage presence to get picked for big roles; she enjoys sport but is un-coordinated (I have toyed with the possibility of whether we should seek dyspraxia diagnosis) so does not get selected for teams, her lack of co-ordination also mean she is not artistic (in the traditional sense) and she has inherited her parents' lack of any kind of musical gene. The other children include her twin sister, who does get selected for sports teams, drama roles etc!
I have tried to encourage many hobbies over the years with no real success (lots of things she quite enjoys but nothing she really shines at).
I think the difference, however, is that she is happy to join in even if she is not good at stuff and is happy to potter around amusing herself when her sister is off doing other stuff. In some ways she is more content and self-possessed than her sister. I do worry about her (e.g. her sister gets more social invitations than she does), but I suspect I probably don't need to - I am probably viewing her by reference to my own personality (eg I would have been upset at school not to be selected for something when I had tried hard or to miss out on invitations), when in fact her personality is different.
Not sure what point I am trying to make, maybe just to accept that he enjoys his x-box so let him have that pleasure. Could you think about taking it on holiday, for example, (some hotels even have them available) and letting him spend time on it, subject to him joining in other stuff. The familiarity might help.