Here's a short list of things I would like to study or do if I only had the time, in no particular order:
Piano, saxophone, geology, astronomy, japanese, game development on old consoles, hiking, weight training, personal site redesign, writing novels, writing stories, designing board and card games, mobile app development, virtual reality development, drawing, composing music, game production and publishing, cooking, etc.
It should be noted that for all of these things listed there was at least a small period of my life where I spent a good chunk of time doing them.
Instead right now I seem to only have the time, energy, and motivation for board game design (and recording it in a diary), keeping my puppy active and happy (walks, fetch), playing some games, fixing a bug or adding a small feature or two in a mobile app once a week, and writing one short story for an anthology once a year.
And I only work 40 hours a week. When I worked 60+ I didn't have energy to do anything but eat dinner and sleep.