Thanks. I was using the PureOS “Software” app and got an error that it couldn’t find imagemagick or something (I did not write down the error message.) Neither the GTK+ nor the Lucid version would install.
I’ll try from the command line instead. Meanwhile I booted my old PureOS installation to get some work done. My old PureOS /etc/apt/sources.list has only one line, too, so that’s not the problem.