My list of winter things to do (I know they are bespoke but OP asked for ideas):
Declutter the kid's enormous pile of old school books, intention is to keep a couple of bits from each child from each school year and recycle/bin the rest.
Sort out a couple/few photo albums. As with everyone I have about 100,000 digital photos so need to get a selection printed out into albums.
And sort out house admin, shread old insurance documents that sort of thing.
Make some linen clothes for next summer, summers are not going to get cooler, I like linen but struggle to find what I want when I want it so I will make some if I start in winter I might have something by the summer.
Learn how to play one or two songs on piano, something fun, George Michael or Guns'n'Roses. Total beginner but everyone has to start somewhere.
I like the relatively new solve the murder case file games, you get suspect photos and autopsy reports etc and play detective. I have a couple of these to play then pass on.
Master Indian chai from scratch.
Will still go out, walks, panto, theatre, exercise and read.