Can't update from 19.04 to 19.10

Question

sudo apt-get update

gives me this error:

Err:20 http://ppa.launchpad.net/gnome3-team/gnome3/ubuntu disco Release
  404  Not Found [IP: 91.189.95.83 80]
Reading package lists... Done                      
E: The repository 'http://ppa.launchpad.net/gnome3-team/gnome3/ubuntu disco Release' does not have a Release file.

I don't know if this is related but sudo in general also gives me this error:

   Traceback (most recent call last):
  File "/lib/security/howdy/compare.py", line 17, in <module>
    import cv2
ModuleNotFoundError: No module named 'cv2'
Unknown error: 1

Answer 1

http://ppa.launchpad.net/gnome3-team/gnome3/ubuntu is a very old repo, and their last release was for bionic (not disco).

You can do no wrong by opening Software & Updates, and deleting that PPA.