As title I was trying gamescope fsr upscaling and comparing it with fsr-hack one.
While fsr-hack cause a 20fps drop, gamescope did nothing, even comparing screenshoots with in-game scaling looks the same.
Also the game still "see" the screen resolution as whole.
Gamescope also works with baldurs gate, linux native.
I attached logs from BioShock Infinite (Epic), Deus Ex GOTY (GOG), Tomb Raider Aniversary (GOG).