Upgrading Ubuntu release from 22.04 to a new version fails with a warning that the Release for qgis does not exist and the upgrade fails.
sudo do-release-upgrade
Checking for a new Ubuntu release
Hit http://security.ubuntu.com/ubuntu jammy-security InRelease
Hit https://dl.google.com/linux/chrome/deb stable InRelease
Ign https://ubuntu.qgis.org/ubuntu-ltr your-distributions-codename InRelease
Err https://ubuntu.qgis.org/ubuntu-ltr your-distributions-codename Release 
404  Not Found [IP: 144.76.174.102 443]
Updating packages lists
E: The repository ‘https://qgis.org/ubuntu-ltr your-distributions-codename Release’ does not have a Release file.
Warning:  apt-get update failed for some reason
Error during update
A problem occurred during the update. This is usually some sort of
network problem, please check your network connection and retry.

Removing qgis does not resolve the problem.
Doing an autoremove to purge unneeded packages does not resolve the problem.
ppa-purge does not resolve the problem.
Clearly there is a sources file somewhere that has not been removed.
The qgis.sources file is not found in the location stated in on-line resources.

Use grep to search for the file.
sudo grep -rnwI ‘/etc/’ -e ‘qgis‘
Files are found in subdirectories not mentioned in online searches thus far
/etc/mime.types:1534:application/x-qgis 
/etc/default/qgis:1:# Options to pass to qgis
/etc/apt/sources.list.d/qgis.sources:2:URIs: https://qgis.org/ubuntu-ltr
/etc/apt/sources.list.d/qgis.sources:6:Signed-By: /etc/apt/keyrings/qgis-archive-keyring.gpg

Removing the qgis.sources and qgis files allowed an update to the new OS version to proceed.