upgrade to 24.04 not working

https://deb.librewolf.net/

States:
Warning: https://deb.librewolf is deprecated and will no longer be updated. Please follow our Migration Guide to use https://repo.librewolf.net instead

So change the repo you have

Thanks, tried changing following the instructions at: https://librewolf.net/debian-migration/. The command sudo apt update && sudo apt install extrepo -y is followed by the error message
E: Failed to fetch http://0ms.run/mirrors/ubuntu/dists/jammy/InRelease Clearsigned file is not valid, got 'NOSPLIT' (does the network require authentication?)
E: The repository 'http://0ms.run/mirrors/ubuntu jammy InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
Assumingly, nothing has happened to remedy the situation, since the next command results in: extrepo: command not found

I suggest you remove that. The domain goes to a parking page.
Should be OK then

Thanks, what do you mean by remove THAT? What to remove and how?

If you run:

sudo grep -r 0ms /etc/apt/*

What is the output please?

Here it is:
/etc/apt/sources.list.d/nala-sources.list.distUpgrade:deb http://0ms.run/mirrors/ubuntu/ jammy main restricted universe multiverse
/etc/apt/sources.list.d/nala-sources.list.save:deb http://0ms.run/mirrors/ubuntu/ jammy main restricted universe multiverse
/etc/apt/sources.list.d/nala-sources.list:deb http://0ms.run/mirrors/ubuntu/ jammy main restricted universe multiverse
Much appreciate your effort

It went smooth until files could not be downloaded. No recovery possible at that stage, also unable to transmit error message due to failure. Thanks for trying, though