I managed to clean up the damage I used efibootmgr to delete the EFI boot entries on the Windows drive
I then booted an Ubuntu USB stick, followed Gentoo's guide for mounting and chrooting into the Ubuntu environment I needed to fix https://wiki.gentoo.org/wiki/Handbook:AMD64/Installation/Base
I then did grub-install --target=x86_64-efi --efi-directory=/boot/efi, where /boot/efi had my external drive's EFI partition mounted up https://wiki.gentoo.org/wiki/Handbook:AMD64/Installation/Bootloader
I checked the drive with efibootmgr to make sure Grub installed right, it did.
This is a really critical bug for any desktop user...
I managed to clean up the damage
I used efibootmgr to delete the EFI boot entries on the Windows drive
I then booted an Ubuntu USB stick, followed Gentoo's guide for mounting and chrooting into the Ubuntu environment I needed to fix /wiki.gentoo. org/wiki/ Handbook: AMD64/Installat ion/Base
https:/
I then did grub-install --target=x86_64-efi --efi-directory =/boot/ efi, where /boot/efi had my external drive's EFI partition mounted up /wiki.gentoo. org/wiki/ Handbook: AMD64/Installat ion/Bootloader
https:/
I checked the drive with efibootmgr to make sure Grub installed right, it did.
This is a really critical bug for any desktop user...