It’s pretty hard to totally “crash” a running Linux kernel, so understanding some details about what symptoms happened, during, and after (screen freezes, sound stops, mouse stops…etc) would be helpful to discern if this was a kernel thing, or just apps crashing. Almost always ends up being a hardware issue or resource constraint though.
As for game logs and crashing, here are some guides and info:
https://steamcommunity.com/sharedfiles/filedetails/?id=3287870137 (This shows some debug steps in detail) https://github.com/ValveSoftware/Proton/issues/6650 https://bbs.archlinux.org/viewtopic.php?id=285102





What kind of machine is this? If it’s something like an HP/Dell/Lenovo, it may have a boot blocker enabled somehow. It wouldn’t make a whole lot of sense since you managed to install Ubuntu, but they may possibly be creating different types of boot volumes.
You’d normally see a message like “HP Sure Start” at the boot screen, for example.