The new Micro~~soft~~slop copilot key always sends the following key-sequence when pressed down:
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.
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 + letter key" can work as expected
I use it as a Compose key, but it's just because it's there; I also did something similar with the Scroll Lock key (I repurposed it to signal "turn it off" for certain autoclicking scripts, otherwise it would be completely useless). IMO keyboards are all fucking wrong anyway.