Emacs 28 captures C-;

Since upgrading from Emacs 26 to Emacs 28 I cannot bind the C-; or C-. commands. When I call the C-; command, a little box with an "|e" pops up on the screen instead and I don't know how to easily disable this popup. Using the help function C-h k before entering C-; does not seem to give any information!

Check your desktop environment settings. GNOME does this for C-.. It could be that the DE or OS also updated and added the new hotkey.

Exactly, it's a quick emoji insert or something along these lines.

The situation you describe is _not_ Emacs 28 capturing C-;, on the contrary: it's Emacs 28 not receiving the keystroke at all! It's probably your operating system capturing C-;, it might be possible to disable this but the instructions would definitely be specific to the operating system and window manager you are using.

Thank you, this must be the issue!

Thank you, it indeed seems to be quick emoji insert, which I can (probably) disable.

If you have gnome, try messing around with gnome-tweaks. I had the same problem some time ago.

Test this by pressing C-h k C-; If emacs is unable to read this key then the key prompt will remain silent

If I recall correctly you can change this in the keyboard shortcut settings in GNOME

As others said it's a Gnome issue. Here is an helpful article how to disable it https://emacsnotes.wordpress.com/2022/08/16/who-stole-c-c-and-possibly-other-keys-from-my-emacs/

Easiest way to turn off, run these commands: gsettings set org.freedesktop.ibus.panel.emoji hotkey "[]" gsettings set org.freedesktop.ibus.panel.emoji unicode-hotkey "[]"