Running TerminalUI app in Supervisor

[dawinaj]

Hello,
I am making a program with Text UI (via FTXUI).
It runs fine when standalone:

But when I try to run it in supervisor, the window is much smaller:

I tried adding DISPLAY to environment= but it didn't do anything.
Any idea how to make it fullscreen, or if it's impossible? I guess fging from two different screens would be quite troublesome...