I had the same error. It had been working fine but I can tell you what I did that broke it. I noticed that I had the "backports" repository checked in the "other software" tab, so I unchecked that. I exited the app then tried to restart it to check that the change had taken, but I got exactly the same error as the traceback above.
I guess something weird had happened to the file /etc/apt/sources.list.d/ubuntu.sources , and that caused the execution path through the software properties app to hit the line with a syntax error. My ubuntu.sources file was a mess with a whole bunch of disabled sources from earlier version of Kubuntu that I'd upgraded from in the past. So I copied the /etc/apt directory from a clean installation of Kubuntu 26.04 that I had elsewhere, and that allowed software- properties-qt to start. I noticed that the "other software" tab no longer had the "backports" option, so that must have been a peculiarity of the past upgrades. A bit of experimentation showed that the correct way to remove the "backports" repository is now to go to the "updates" tab, and uncheck "unsupported updates". That works fine. So it seems that if you've got a mess of obsolete stuff in ubuntu.sources, that might be the problem. There's still a syntax error in software-properties-qt, but you won't hit it if you have a clean ubuntu.sources like this: Types: deb URIs: http://archive.ubuntu.com/ubuntu Suites: resolute resolute-updates resolute-backports Components: main universe restricted multiverse Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg Types: deb URIs: http://security.ubuntu.com/ubuntu/ Suites: resolute-security Components: main universe restricted multiverse Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2154196 Title: Software properties qt wont launch because of syntax errors in its code - Kubuntu 26.04 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/software-properties/+bug/2154196/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
