So, I hate being "made" to join in games or being told I am "spoiling the fun". I'm also not that keen on films . However I'm really happy for others in the group to play and I'll observe or take myself off for a bit to read a book or whatever.
I think there are 2 different issues here.
He doesn't like enforced "fun" - fair enough, no-one should be made to do something if it is making them cringe inside.
He tends to monologue on and on. - not such fun and will definitely make your kids want to retreat to their screens.
I think you could have a range of games to play with short gaps in between for him to talk !
"Uncle Geoff, you know we love having you for Christmas and I look forward to having a chat. We do like to play some games as a family though, but I don't want you to feel like you have to join in at all if it isn't your thing.
Then plan- immediately after lunch, 20 minutes chat with coffee and chocolates. Then, family game of charades ( Uncle Geoff, is this your thing? Otherwise maybe you'd like to hand out the titles or if you'd like a bit of quiet I've recorded Carols from Kings/got some great gardening magazines/Christmas edition of Private Eye/New Scientist and you could enjoy them in peace in the comfy chair in X room. I'll put the kettle on again at about y o'clock.)
Then encourage him to join again for refreshments for 30 mins and then do your cracker mystery game etc. Each time offer him the option of joining in or not depending on what he prefers!
You might want to give him the heads up beforehand. ( Uncle Geoff, we love your company at Christmas and we also really do want to do things as a family on Christmas afternoon. What with work/school/euphonium practice/Steve's microbrewery and looking after the alpacas, we get so little time when we are all together these days The kids are at that awkward age though where they tend to just disappear on screens if we aren't careful. We've found they do enjoy xy games though so we want to spend some time doing that. I know that maybe isn't your cup of tea so feel free to join in or not depending on how you feel. We will still have plenty of time for coffee and chat. I'm getting lots of mince pies/m and m's/Pringles/parsnip flavoured candies as I know they are your favourite.)