Comment 5 for bug 2053228

I have the same issue for software-properties-gtk. Software-properties-qt does start, but doesn't show any software sources as enabled.

If I had to guess, I'd blame the fact that upgrading to 24.04 seems to have moved default repos from /etc/apt/sources.list to /etc/apt/sources.list.d/ubuntu.sources and changed the format to the one specified in deb822. Attached here is my /etc/apt/sources.list.d/ubuntu.sources

upd: found this change that probably caused this bug: https://discourse.ubuntu.com/t/spec-apt-deb822-sources-by-default/29333