I'm taking this a little bit back to around a decade ago when Runescape was in full flow, at least for me and my friends at the time. That game has some grind, and personally my favorite thing to do was to start a music playlist and just start adding songs, looking for new songs and just getting lost. It's enjoyable enough to get you through hours of mindless grind, and gives enough time to those 1 or 2 clicks needed every 3-5 minutes or so.
Genuinely, music is not too important to me and most of my favorite songs were discovered during those years just because I had the time to research new stuff.
If that doesn't float your boat, then of course you can crack out that novel that you've been meaning to read and start on it. Managed to work my way through most of the DragonLance Chronicles in that time period as well. Ah how I miss free time.