[Post-Install] Keyboard and mouse not working post installation of 26.04 (after upgrade from 25.04)

[notAProgrammer]

I updated from 25.04 or 25.10 to 26.04, and now my in built keyboard and mouse aren't working. They are however, working in the grub menu.In addition, the power button is correctly turning the system off.

I have two kernels - 7.0.0-27-generic - 6.17.0-40-generic. Trying to boot into the recovery mode (graphical) of the older 6.17.0-40 still leaves me with the same problem in the graphical interface. However, in recovery mode during terminal usage as root, I'm able to perform all standard I/O operations.

Any advice on what to do next?

[notAProgrammer]

[Fixed]

I sorted this out by first figuring out what the running display manager was. Now, from the root terminal area, no graphical interface was online. So I couldn't do something like

systemctl status sddm

Instead, I catted the display manager area:

cat /etc/X11/default-display-manager

After finding that the system was using sddm, I checked the config file in /etc/sddm.conf. The new isntall for some reason decided I would like to use an x11 display servers, even though my previous version (and rest of my laptop) run on Wayland.

Catting the config file:

$ cat /etc/sddm.conf
[Autologin]
Session=plasma

[General]
DisplayServer=x11

Which was a fun surprise. I swapped the DisplayServer to wayland to get it running again.

As a fast workaround you can also run:

plasmastart-wayland

In order to access your actual graphical interface (post login) and then backup your files or something.

Good luck!