[tde-users] Display configuration troubles

I use a Lenovo X390, MX-Linux 21.3, with one user using xfce (the "original" DE) and the other using TDE. When I plug in HDMI (for a beamer, in this case), xfce can easily be set up to mirror the display. When I use TDE and connect the Beamer (seen as HDMI-2), TDE automatically extends my screen to the beamer. xrandr -- output HDMI-2 --same-as eDP1 (where eDP-1 is the internal screen) does mirror the screen, but it remains extended. Now if I run "Configure Displays" and select "Enable local Display control for this session" (which was not activated), I do get the mirroring I am looking for. But if I click "Apply" the screen turn to psychedelic colours - seems to be wating for me to validate the choice, what I can't do and anyway would not as it's unusable. After a while the sceens returns to my desktop, albeit stil psychedelic, and I must log out / log in to get my desktop back. So for the time being that means I have to use xfce when I need the beamer. Anyone knows what's going on and what I should do to mirror my 1920x1080 screen to the HDMI beamer? Thierry