Disabling secure boot after it had already started happening didn’t do anything;
redoing the installation, rebooting, having it happen again, and re-disabling secure reboot also didn’t fix it;
redoing the installation again and immediately disabling secure boot upon the first reboot did, though. Bazzite booted properly and I got to the desktop.
I the turned the computer off and back on to make sure I could get in normally. There are now four different Bazzite options on the GRUB screen that pops up on boot, but if it sits for a few seconds it selects the first one and I end up at the desktop again.
Fixed, I think?