It's interesting, but I think hobbies and interests are the way to go.
With my PIL, MIL had been a SAHM and then worked PT for years, so had charities and voluntary organisations she was involved with, so just carried on with that when she retired from her PT job. FIL was big into golf, and MIL encouraged him to take on more of the organising side of club events, plus he went part time for a couple of years before retirement to ease into it.
On the other side, both my parents worked full time in high pressure careers until retiring early, they didn't really have time or energy for hobbies, so didn't have a big network or things they did. They retired and seemed to get old straight away. (PIL are older but you wouldn't think it if they were all in the same room.)
From that, I've taken it's important to have hobbies and interests, stuff to do out of the house, it doesn't have to be joint.
Christmas is different because all the normal things aren't going on.
There's a reason there's lots of newly retired people volunteering in charity shops and going into schools to hear children read, or arranging clubs and societies.
Stopping paid work and doing nothing are different things.