For some time I've been unable to launch Northgard on the Steam Deck while the game has launched just fine on my desktop Manjaro. Decided to test again and stumbled upon a solution by reading the logs and with some trial and error.

This is the error message I received that resulted in a segfault:
> SIGNAL 11
> sdl.$Window.__constructor__(sdl/Window.hx:74)
> hxd.$Window.__constructor__(hxd/Window.hl.hx:100)
> hxd.$System.start(hxd/System.hl.hx:117)
> hxd.$App.__constructor__(hxd/App.hx:45)
> $AppBase.__constructor__(AppBase.hx:1)
> ui.$TitleScreen.__constructor__(ui/TitleScreen.hx:67)
> $Game.main(Game.hx:4726)
> .init(AlphaOutlinePass.hx:2)

After fiddling with Lutris' settings I eventually found out that the game doesn't actually load the game's provided libSDL dynamic library and that seems to trigger the crash.

The solution is rather simple: Setting "Preload library" option under Northgard's Game options in Lutris to point to libSDL2-2.0.so inside the game folder (Northgard/game/libSDL2-2.0.so) fixes launching of the game.