Installing the kde-standard package is not what you would like to install in the first place as a user who wants to have fine grained control over the packages on your system. Given the large list of things that you do not want, I would recommend removing kde-standard and install plasma-kde-desktop. The latter is like a minimal kde.
However, we can ...
it happened to me too.
I returned to the buster:
deb http://alcateia.ufscar.br/debian/ buster main non-free contrib
So, I made this:
sudo apt purge kde* plasma* tasksel*
sudo apt autoremove --purge
sudo apt install tasksel
sudo apt install task-kde-desktop task-desktop task-print-server task-ssh-server
I got back to buster ...
No, that's not correct. /etc/fstab is supposed to be world readable. A LOT of programs depend on this, and it's world readable on every standard Linux distribution. You're not supposed to put credentials or anything else that's actually sensitive in this file (see Does /etc/fstab need to be world readable? for how to avoid this), and hiding anything else in ...
This isn't an answer, strictly speaking, but I didn't want it to get buried in the existing comment section:
This appears like it would work: it adds a display setting that's listed by xrandr and then the new size is available in KDE's system settings... but when I select it in the system settings gui and click 'apply' it resets back to the previously ...