(I don't actually use gamescope since I've had trouble with it).
Empty error log. Regular logs look fine (attached). Game runs fine once it finishes loading. Game is stored on an HDD, but every now and then the game will launch just fine in under a minute or two as expected, so that's not the issue (and I've had the game on this drive for years with no issues back when I used Windows). When the game is loading, it's just a black screen with the red valve logo. Eventually it starts to load the video (which is completely borked so just shows the first frame for a long time). After that, the main screen ui has that first frame overlayed on top while it finishes loading (ui is only sometimes interactable in this state). Once that clears up, the game is completely fine (except for a foliage flickering bug which might be a driver issue). This whole process takes at least 5 minutes, up to about 10 minutes.