Can't activate MangoHud

Lutris 0.5.14 (Flatpak)
MangoHud Version 0.7.0 downloaded from GitHub and installed via “./ install”
Granted access to xdg-config/MangoHud:ro via Flatseal
FPS counter (MangoHud) trigger is inactive.

You need to install the flatpak version into the 23.08 area - instructions are on the mangohud git site

What is MangoHud? Do I need it on my Steam Deck?

It’s an overlay that shows you information like FPS, CPU/GPU temps and whatnot while you play

It also allows for you to force vsync, or just a straight FPS limit

You don’t necessarily need it.