Great question @Anonymous .
For years I have been involved in various online forums. Many contacts from those gravitated over the years to Facebook and for a while I was offering asynchronous classes via Facebook. Not doing that anymore, but still have contact with 100s of people there. So during isolation, it's been a blessing to be able to chat and joke with internet friends just like usual.
I've taken several writing workshops online and via Zoom, and have done a couple of the Writers' Digest prompt challenges where a host provides a word each day for a month and participates write a poem or flash fiction on that prompt. Those are fun, great discipline and mental / creative exercise, and totally free.
I've sought out old classmates I grew up with since kindergarten and worked on developing renewed friendships.
I've tried to sort through closets and drawers and take stuff to Goodwill-like charities. Now thinking about doing the same with old paper files like tax returns and old receipts that are no longer needed or can be digitized.
And I started an iPhone photography course, which got me out of the house and walking for a while, but I didn't keep that up. Need to get back to that!
My daughter has been training a service dog during this past year, mostly from free videos on YouTube. She got him as a 2 month old, I think, so he's still a pup. Her biggest challenge is keeping strangers from wanting to play with him when they are out at a store, even when he's wearing his service dog in training vest. Big no-no. That's forcing her to learn more assertive skills for herself too.