Keyboard input gets ignored since Proton 6.3 when hitting ctrl+shift+e or ctrl+shift+u

System Information

• GPU: RTX 3080
• Driver/LLVM version: nvidia 470.42.01
• Kernel version: 5.4.0
• Link to full system information report as Gist
• Proton version: 6.3-5

I confirm:

• that I haven't found an existing report for this issue.
• that I have checked whether there are updates for my system available.

Symptoms

In Everspace 2 it happened to me, that after a certain key combination the space ship stopped accepting keyboard input. After pressing random keys it somehow worked again, but for a while I wasn't able to figure out which combination it was. After verifying it doesn't happen on Windows and being able to reduce the keys in question that cause this issue, I figured out it happens when I press the combination left ctrl + left shift + e. I was able to confirm this also happens in the game GTFO. This allowed me to google for that shorcut and lead me to the emoji and unicode input: https://askubuntu.com/questions/1083913/what-does-ctrl-shift-e-do-while-typing-text/1159087#1159087

Reproduction

When hitting the shortcut ctrl+shift+e or ctrl+shift+u in games using Proton 6.3 most keys are getting ignored until you hit enter or esc. When pressing ctrl+shift+e and space a menu pops up in the bottom left corner.

This does not happen with Proton 5.13 (tested with Everspace 2).

Workaround

Workaround for me is to start ibus-setup via terminal, open the emoji tab and remove both shortcuts.

Start by reproducing the ctrl+shift+e and ctrl+shift+u behavior in Everspace 2 or GTFO under Proton 6.3, then compare it with Proton 5.13. Check the ibus-setup shortcut workaround and Proton's keyboard-input behavior; done means those shortcuts no longer suppress game input or open the bottom-left menu.