Get the flatpak. It's less buggy. There's a weird flicker, fullscreen is broken, and there are no keyboard shortcuts.
On Mint 20.1 Xfce and the moment I go full screen there is no way of exiting full screen. Bummer cuz I love NEStopia on Windows. Higan seems like a good alternative without issues like this.
Unable to separate the controller from keyboard user. Only has 2 player / 2 controller support, meaning you won't be able to play some games which support 3 - 4 players.