You can't even change brightness on lockscreen when using a notebook or laptop.

As someone who runs multiple desktop sessions at once, each on a different virtual console, sddm is a continual pain in my workflow. Notably:

• It assigns desktop sessions to virtual consoles inconsistently, and has no way to manually configure them, so Control+Alt+FN often switches to a session that's not the one I wanted. The assignments can change from day to day or any time a session logs out and back in. This makes using multiple desktops a constant pain.
• I don't know for sure, but I suspect it is behind the graphical glitch that makes the desktop session unlock screen draw incredibly slowly on KDE 5. Having to wait several seconds for each character in my passphrase to register is an annoying waste of time.

im not up on the latest lore admittedly but looking at the github repo, it seems there has been little activity in terms of new code. Its also not well integrated with KDE despite it being primarily used by KDE Plasma.