As far as I know, that only stops out of date versions of grub that have a certain vulnerability from running that would allow escaping Secure Boot. Meh. It doesn’t touch any Linux files or anything and you can boot if you turn off Secure Boot so you can fix it. Long shot from what used to happen where you could only have one boot loader installed at a time so installing Windows would wipe what was there before.
(and by fix it I mean replace grub with systemd-boot)