Samsung DEX

I have samsung galaxy8 and samsung dex - to connect smartphone to big display.
When I connect by samsung dex, app is not working in full display. I modify app with dex max, and app is work on display now, but I can’t loggin =( Video

I was able to run Zwift on fullscreen with the built in Experimental Features of Dex. From there, I was able to run the game normally, including login.