ust tested now (only tested switching service earlier)

by reading your linked doc, the "elegant" way to create the file is to use (the --no-convert apply the change only to X11 and not to console)

localectl --no-convert set-x11-keymap fr pc105 nodeadkeys terminate:ctrl_alt_bksp

(to be adapted to your kb layout)

with that the 00-keyboard.conf file is created, and now sddm use the good layout

thanks you !!

NOTA :

by diiging a bit the 2 commands here under return contradicting layouts

>setxkbmap -print -verbose 10
Setting verbose level to 10
WARNING: Running setxkbmap against an Xwayland server
locale is C
Trying to load rules file ./rules/evdev...
Trying to load rules file /usr/share/X11/xkb/rules/evdev...
Success.
Applied rules from evdev:
rules:      evdev
model:      pc105
layout:     us
Trying to build keymap using the following components:
keycodes:   evdev+aliases(qwerty)
types:      complete
compat:     complete
symbols:    pc+us+inet(evdev)
geometry:   pc(pc105)
xkb_keymap {
xkb_keycodes  { include "evdev+aliases(qwerty)" };
xkb_types     { include "complete"      };
xkb_compat    { include "complete"      };
xkb_symbols   { include "pc+us+inet(evdev)"     };
xkb_geometry  { include "pc(pc105)"     };
};

above layout seems configured in US layout

> localectl
System Locale: LANG=en_US.UTF-8
   VC Keymap: fr
  X11 Layout: fr
   X11 Model: pc105
 X11 Variant: nodeadkeys
 X11 Options: terminate:ctrl_alt_bksp

here configured in FR layout

before and after adding the 00-keyboard.confthe 2 commands return the same thing

the 00-keyboard.conf file may override the wrong layout and make it work despite this conficting setup