When I booted up Ubuntu 22.04 it worked, but autocompletion in Eclipse 2023-09 has disappeared. Whenever I try to autocomplete with Ctrl + Space or try to access a method from an object with ".", nothing shows up. Also, when trying to fix an error via the Quick Fix shortcut (Ctrl + 1), nothing happens either (I have to go to the "Problems" tab and right click the error to be able to quick-fix it. Hovering over warnings or errors in the text editor displays an empty box.
Windows -> Preferences -> Java -> Editor -> Content Assist -> Auto Activation is enabled. Proposal Kinds in Advanced are also checked. No solution after restarting the IDE, reinstalling it or rebooting the system.
EDIT 10/18/2023: Ctrl + Space is already key-bound in dialogs and windows, but when trying add to add the binding in the General -> Keys section as @howlger suggested, the combination's not recognised. Something in the system is catching the combination, but I can't understand what.
Solved. Looks like the keyboard I connected the laptop to was the responsible of the confusion. I just unplugged it and it works fine. Thanks everybody