awesomehaircut wrote:The way to login as root to kf5 is by modifying MinimumUid to 0
in /etc/sddm.conf (or creating it with sddm --example-config and moving it to /etc/sddm.conf)
[…]

As already pointed out in this thread - one should never start an X session as root!
sddm doesn't enable root login by default for a reason.

eliasp wrote:sddm doesn't enable root login by default for a reason.

sddm doesn't allowed users with a user id lower than a thousand for a reason. The reason being to avoid clutter and hide most account a user need not worry about.

Login in as root is a choice to be made by a user, not dictated by a distribution, platform or Desktop Manager.

awesomehaircut wrote:Login in as root is a choice to be made by a user, not dictated by a distribution, platform or Desktop Manager.

your choice of display manager is not dictated and there are a number to choose from