I mainly use Hammerspoon as I prefer Lua over Json. I find Lua far easier to modify... to be fair, both Hammerspoon and Karabiner Elements have quite an impressive repository. If you want to do something it is probably already done.
My favourite is probably swapping of Cmd to Ctrl in VMs. That way you can use keybinds in Linux or Windows VM with the same muscle memory as in macOS. It may get confusing if you use Super a lot in Windows/Linux.
Another one is rebinding right Option (or "Alt") to Hyper. Most of the keybinds I use I got from this repo . Though I did make quite some modifications I found it a good starting point (merging my own back). I remap Caps to Escape and Ctrl (latter if combined with another key) via Hammerspoon. You could also use Karabiner Elements though. Although I still use Caps mainly for Esc (muscle memory...)
On a Windows computer, I used AutoHotKey for some other stuff (gaming related QoL improvements). For some reason, Blizzard decided that in WoW you are not allowed to spam a key if you hold it. Which is flat out painful for the hands. I no longer play WoW regularly though. If I do, it is via Wine (on a Linux desktop). In Diablo 3 I made a keybind to swap gearsets. This was before Blizzard implemented the wardrobe.