X11 package is disabled by default in Fedora KDE, so we install it back:

sudo dnf install plasma-workspace-x11 kwin-x11

Then, it should be enabled in SDDM configuration. We need to edit /etc/sddm.conf:

# Control x11/wayland startup
# DisplayServer=wayland
DisplayServer=x11

Optionally, it may be needed to select Plasma (X11) desktop in the SDDM greetings window.

P. S. Still I do not undestand why Insynk does not work with the default Wayland and requires X11 configuration to sync google drive accounts.