Old OS remains in my Boot Order settings in BIOS

[wooden bone]

First, it's recommended to fo a clean install. Second, don't use memejaro

.s manjaro

[long palm]

Reasons to not use Manjaro:
• https://github.com/arindas/manjarno
• https://www.hadet.dev/Manjaro-Bad
• https://rentry.co/manjaro-controversies
• https://manjarno.snorlax.sh
• https://averagelinuxuser.com/manjaro-review

[zinc shell]

you can remove the entry with
efibootmgr -B entrynumber