How I fixed all new windows not accepting keyboard input on Ubuntu

Problem

When restarting my computer from standby, after some time working regularly, I noticed that at a certain point, every single window I newly opened was not accepting any keyboard inputs.

The windows were accepting mouse clicks and copy/paste worked fine, but I could not type anything in any of the new windows.

Solution

While I noticed that restarting the computer, or restarting the window manager (sddm in my case) fixed the problem, this was extremely tedious since I had to re-open every single application after the restart.

Instead, I found out that the issue was that the ibus daemon crashed, possibly related to a segfault in the NVidia proprietary graphics driver.

Once that was clear, the solution was simple: Run

ibus start

in a terminal on the graphical interface, or run

DISPLAY=:0 ibus start

if you don’t have access to a console on the desktop where you can enter stuff.

This command will not print anything, but you will have immediate keyboard input in all new windows again.