I am running linux and have no problems running the game at max settings.
For the last week though, Divinity will not run if steam is running. For a few days it was OK if I ran outside of steam (by manually triggering the "runner.sh" file in the game directory) - but it suddenly started complaining about a lack of libsteam_api.so - which I plundered a copy of from another game's folder.
Not it will not even run if Steam is going in the background. I have to make sure that I quit Steam COMPLETELY before I run the game, and only then will it work....
I get a fairly detailed error in Steam when I try to launch it - here it is: