Haven't really had any problems so far in regards to crashing, that being both on Intel and AMD with a 4070 and 3060ti.
Sure a few texture glitches and some loading ship animations have been a bit glitched, and the occasionally ragdoll enemy leads to stuck in geometry, but otherwise it seems mostly fine after some 20-30 hours.
What I find much more egregious is the amount of loading screens, combined with ship combat just plain being boring/being too hard in the starter ship.
I am not using it with immutable config, so the only thing flatcar is doing is it has an A and a B partition for /usr that it switches between on updates (such that it can always rollback to the last working system).
I only used ignition for the initial setup, after that I just ssh in to the machine and change systemd services via /etc/systemd/system (such as added new mounts, using systemd unit's for running docker containers etc.)
Adding a user is initially done: https://www.flatcar.org/docs/latest/setup/customization/adding-users/
The idea is that all software you need to run except for systemd and some utilities (more or less what is in busybox) are run in containers, which i think was the same deal with RancerOS.
It is a fork of CoreOS, from when they got bought by RedHat and it was abandoned (or rather morphed into being fedora based).
It is has been fairly stable for me over the past two+ years, with one systemd-resolver snarfu. The auto update being baked in from the get go is nice.
Only thing to be aware of is that Kinvolk who are the maintainers have been bought by Microsoft, though so far it has not affected anything. Also if you don't like systemd then it is not for you, as that is more or less all the distribution is.
They are running docker 20.10.23 on the stable branch atm. https://www.flatcar.org/releases
Ah yeah ok, I had longer loading times on my 9700k, so yeah the series S might be hard pressed. The bugs you describe sounds annoying as hell.
Quest breaking I have luckily not run into (yet), but I have started getting the same outposts over and over on different planets. The good old mass effect board the exact same ship, which makes sense in universe but gets a bit dull after first couple.