@ZaeNae I’m suspicious that you had an incomplete upgrade. Even though you were able to boot by manually changing the version in grub, that shouldn’t have been necessary, and it seems to indicate that the upgrade to 6.10 did not finish.
I would look here for steps to fix.
When you edit grub while booting, those changes will not persist to the next boot. You can see here on Arch Wiki for making changes to grub configuration, but I really think your issue is a broken upgrade.