For everyone who have performance issues on intel+nvidia (optimus) laptops. Game running on Intel GPU by default, to change it follow the instaruction:

1. Find settings.json somewhere in !/.local/share/Steam/steamapps/compatdata/704270/pfx/drive_c/users/steamuser/Documents/Avalanche Studios/GenerationZero/Saves/settings/
2. Change "DisplayDxAdapter" value from -1 to 0 - looks like that will force game to use proper GPU, at least in my case frame rate jumped from 3 on LOW to 40+ on ULTRA.

Game itself does not choose proper GPU. Same troubles in Window, where you need to force use Nvidia GPU via Nvidia settings.