I'm pretty sure most login managers have a drop-down hidden somewhere where you can select what desktop manager it launches once you log in.

I think you could just enable GDM and choose KDE on login. It should remember your choice.

Could anyone explain to me how to set it up so you can login using your fingerprint? I'm using Bazzite, which is basically just Fedora KDE. Right now I can only do that on the lock screen, but not the login. I haven't been able to figure it out, but OC's comment reminded me about it and I figured I should ask just in case someone happens to know.

It is absolutely possible. Last time I did it, I just had to install the one I wanted and uninstall the one I didn’t.

So, I was wondering if it would be possible to use just the GDM login prompt, but have it feed into KDE desktop and if so what I’d need to tinker with to configure it.

It's definitely possible. As a long time non-KDE/Gnome user I've been using various display managers to log into the window managers of my choice

I think GDM might just have a dropbox somewhere in the corner or the edge of screen where you can choose which WM to spawn after login. So telling it what to spawn should be just a one-time picking

As for the switching from SDDM to GDM, I guess

sudo systemctl enable --now gdm.service -f  
sudo systemctl disable sddm.service # might be not needed due to -f 

Mix and match login managers and desktop environments

So, I was wondering if it would be possible to use just the GDM login prompt, but have it feed into KDE desktop and if so what I’d need to tinker with to configure it.

I imagine that it'd depend on the login manager.

I use emptty, which allows me to log in on a text console.

For that login manager, I:

Add a ~/.config/emptty-custom-sessions/sway-wrapped.desktop file:

Name=Wrapped Sway
Exec=/home/tal/bin/my-wrapped-sway.sh
Environment=wayland

And add ~/bin/my-wrapped-sway.sh:

#!/bin/bash

. ~/.bash_profile

export XDG_SESSION_TYPE=wayland

exec dbus-run-session sway "$@"

I mark my-wrapped-sway.sh executable (chmod +x ~/bin/my-wrapped-sway.sh), and done.

searches

https://blog.boristerzic.com/posts/2023-09-17-build-your-own-desktop-environment/

Adding a New Custom Desktop Environment in Arch Linux

Your desktop environment is typically started right after your login to the system using your display manager (or login manager). In graphical display managers like gdm you can select one of several session types from a list. This is where we want to add a new entry for our labwc based desktop environment.

On Arch linux these sessions are stored in /usr/share/xsessions in separate .desktop files. A /usr/share/xsessions/labwc.desktop file could look like this:

[Desktop Entry]  
Encoding=UTF-8
Name=labwc
Comment=labwc
Exec=labwc
Type=Application

I'd probably give that a try.

Framework 13 here, KDE Fedora user too. It literally never occurred to me that I could use the fingerprint to log in! Commenting so that whoever answers you can make my day too.