I just checked gnome, KDE and xfce beta live beta.
(Thanks to Ventoy to make it super easy to switch live images)
Tumbleweed I can run :
HDMI - Ryzen 4k 60 Hz
USB-C nvdia 1660ti 4k 60Hz
and internal notebook panel Ryzen 1080p 60HZ
as triple screen configuration.
KDE: If I start 15.4
X11 the USB-C screen shows a static image and I can pull the mouse to the screen but not windows.
wayland I can us the USB-c but only 30Hz
If I mark the USB-C screen as primary, the screens become unresponsive, menu.
Gnome, I cannot use the USB-C as primary. only 30Hz.
XFCE, USB-C 60Hz, but cannot be used as primary.
Where to report this bug?