That’s not an error. That’s the boot menu. You probably hit a button while it was starting. It allows you to enter different boot options or when you have multiple operating systems installed you can choose which one to start.

Just select the first entry and hit enter.

What’s the difference between the first two? Ostree:0 and Ostree:1
Bazzite installs updates by making a snapshot of the entire system and then installing a new system image beside it.
That way if there’s an issue with the updated system, or you broke it, you can just boot into the last known good one.
Ostree:0 is the current system and Ostree:1 is the previous version.