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.

• 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 + letter key" can work as expected