I was in a similar situation with Slackware that used to have lilo bootloader and for uefi "elilo"
i fancied grub2 so i installed it and it works fine.
Once installed if you run :
it should (hopefully) find Os Windows and add it to boot loader
to elaborate a little further in my slackware i have at/boot/grub:
bash-5.0$ tree -L 1 grub
in your Ubuntu you would have something similar; thus when you wipe your Ubuntu your grub config files etc will be wiped also. Probably entries might remain on the EFI partition
ghost entries for os gone you might say.
If you install Pop OS , install grub and run stub update-grub then config files should be found in /boot somewhere