Upgrade to Mint 21 from 20.3 -problems

[Nihao]

Hi all.
I am trying to upgrade to Mint 21 but not having much success.
One of the major problems is that I am not too conversant with the way Linux works but really like using it.
When I try to upgrade and the system checks the APT Cache in a Terminal, I keep getting the following message -

Code: Select all

eading package lists... Done
W: GPG error: https://deb.opera.com/opera-stable stable InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY DD3C368A8DE1B7A0
E: The repository 'https://deb.opera.com/opera-stable stable 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.
E: Failed to fetch http://ppa.launchpad.net/kritalime/ppa/ubuntu/dists/focal/InRelease  403  Forbidden [IP: 2620:2d:4000:1::3e 80]
E: The repository 'http://ppa.launchpad.net/kritalime/ppa/ubuntu focal 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

I do have Opera but do not seem to be able to remove it either
Any help would be muchly appreciated.
Thanks

[Nihao]

A bit more info if it helps
The APT cache shows the following in the terminal

Code: Select all

Reading package lists...
E: Failed to fetch http://ppa.launchpad.net/kritalime/ppa/ubuntu/dists/focal/InRelease  403  Forbidden [IP: 2620:2d:4000:1::3e 80]
E: The repository 'http://ppa.launchpad.net/kritalime/ppa/ubuntu focal InRelease' is not signed.
W: GPG error: https://deb.opera.com/opera-stable stable InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY DD3C368A8DE1B7A0
E: The repository 'https://deb.opera.com/opera-stable stable InRelease' is not signed.
Error - Return code: 100

I hope someone can help.
Thanks

[AndyMH]

The mint upgrade tool is okay if you do not have a lot of "foreign" packages installed. This includes applications installed from deb file, ppa, source or other repos. I have a lot of those.

You easiest solution is to do a fresh install. It's what I do. You can use mint's backup tool to backup your data files (from memory it creates a compressed archive - .tar.gz) save it to another drive. You can also "backup" your applications (software selection) - it creates a list as a text file, think it stores it in $HOME/Documents - copy it somewhere else. When you do a "restore" it will restore anything that is in the mint repos, but not any "foreign" packages. Those you will have to re-install manually.

[Nihao]

Thanks AndyMH. that was the info I was looking for.
Unfortunately I will not have time to install ATM as going on holidays for 6 months and not taking the desktop.
Will try when I get back.

[SMG]

Moderator note: josch's issue can now be found here Upgrade to Mint 21 from 20.3 -problems (Paketquellen gives an error). Please do not add new issues to someone else's topic.