Linux X windows support

We had our app built with 2020.3.23f1, it works in multi-X Window environment well.
But then we updated to latest LTS 2022.3.9f1.
It seems that it does not understand X windows at all.
I made a simple 2d unity app using 2D Core template.
Normally you define with environment variable DISPLAY the window you want to use.
DISPLAY=:0.1 ./display_test.x86_64
If I do this with e.g. xclock, it goes to right X window.
But when I do this with test app, the UI comes to window where I am giving the command. It seems that Unity bypasses X windows somehow.

Does anyone have any experience on multiple X windows with Unity? How it is supposed to work?