Good job. I much prefer the python install. AppImages are clumsy and slow in my opinion. They're also unnecessarily large since they package all their own dependencies, but most of the dependencies are already included in the OS. AppImages also don't give you daemon or CLI options, which I find handy from time to time. I do use AppImages when temporarily booting from a live USB for air-gapped use, but other than that I tend to avoid them.
Maybe I'm just old fashion (in my 70s) but I also prefer a python install over appimages.
I also like the Python install option. I have even made my own .desktop file which I use to launch Electrum graphically on my computer.
PS: The problems experienced in the OP can be solved simply by installing Electrum with the
--user option or by installing inside a virtualenv (
apt install python3-pip python3-venv && python -m venv .env && source .env/bin/activate and then install Electrum normally.