The new Micro~~soft~~slop copilot key always sends the following key-sequence when pressed:
copilot key down: left-shift-down left-meta-down f23-down f23-up left-meta-up left-shift-up
copilot key up: <null>
This means there's no real key-up event when you release the key --> it can't be used (properly) as a modifier like ctrl or alt.
The workaround is to send a pretend key-up event after a time delay, but then you mustn't be too slow / fast when pressing a shortcut.
- Linux workaround: https://github.com/m-bartlett/remap-copilot?tab=readme-ov-file
- Windows workaround https://github.com/randyrants/sharpkeys/issues/560
- https://xcancel.com/dcolascione/status/2019936377408811319
tldr: AI took a perfectly working modifier key from you.
--- edit ---
Some keyboards apparently do the "right" thing and don't send the whole sequence at once, you can remap those properly with keyd, see: https://github.com/rvaiya/keyd/issues/1025#issuecomment-2971556563 / https://github.com/rvaiya/keyd/issues/825
copilot key down: left-shift-down left-meta-down f23-down
copilot key up: f23-up left-meta-up left-shift-up
this will still break left-shift + remapped copilot and left-meta + remapped copilot, but RCtrl remaps should work as expected
The WHATNOW is impossible to properly remap?
Honestly X11 keystroke and modifier management is not that good. Because were it better, you could map any sequence to a different kind of action, possibly intercepting them. Instead you have keystrokes with modifiers, sometimes the keystroke is the modifier key alone. One can work around some things of this with, say, WM menus in FVWM called by one keystroke with modifier and then keybindings for menu items to have something like Emacs UX.
That nuisance you pop off with a flathead screwdriver and throw in the trash can.