I am running Tumbleweed on an ASUS Zenbook Flip S UX371 with both Gnome and KDE Plasma 5 installed. The screen has 4k UHD resolution which makes everything really small, so I had to do a lot of tweaking in KDE to make my system readable, but I couldn’t figure out how to adjust font sizes in the display manager so I just switched to GDM. With GDM, the font sizes are readable.
After the last TW update to 20211012, I can’t use GDM anymore. After a reboot, it won’t let me login to KDE unless I login to Gnome first, then logout, and then login to KDE. So I switched the display manager back to SDDM, but the fonts are tiny, tiny, tiny.
How do you update the font size in the display manager? I looked at SDDM configuration in system settings and couldn’t find anything related to fonts.
What you describe is actually Bug 1191248. Actually, you can login to KDE. But you have to first go to the menu and select “Plasma X11” there. Login to KDE as the cached default doesn’t work. Or you can instead login to “Plasma Wayland”, and then you won’t have to mess with the menu at each login – if Wayland works on your computer.
I’m using SDDM in tumbleweed Xfce.
In KDE System Settings, startup and shutdown,
Login Screen, Synchronize Settings.
just click synchronize settings and click synchronize.
If memory serves it will ask for the root password.
it will set your font and DPI settings to match your settings
in plasma desktop.