1.12.2 - Linux Wayland - fullscreen appears on wrong display

[marp]

XnView MP 1.12.2
Ubuntu 26.04
Wayland
Gnome

Multi-display setup:
Secondary display on left side, primary/main display on right side.

XnView main window appears reliably on the main display (right side).
However, switching to fullscreen, the fullscreen window always appears on the secondary display (right side).
This doesn't work for me, among several reasons, the secondary display is very old, with rather bad color reproduction.

Researching a bit, this seems to be related to the Wayland display server always using POSITIVE value Cartesian coordinates, starting at 0,0 on the upper left (i.e. the upper left of my SECONDARY display).
Apparently, Linux apps are expected to query what is the main display, and adjust default position coordinates for windows accordingly (1920,0 in my case, I guess).

Normal main app (not fullscreen) windows can be automatically adjusted (by Wayland, or GNOME, or Gnome extensions, or whatever) to remember their previous position.
But apparently, that mechanism doesn't work for windows that are created and displayed as fullscreen right from the beginning.

I noticed that there is a Settings option "Dual monitor: Use second monitor".
Toggling this option has zero effect for me - neither on nor off seems to make any difference - it always displays on the secondary/left-hand display.