How to get Windows to show up in OC boot list?

Installed macOS Big Sur on nvme drive. Installed Windows 10 on different SSD. Windows 10 overwrote my EFI on the macOS drive -- no biggy, I just backed it up and put the macOS EFI back. So now I can boot into macOS just fine, but Windows doesn't show up as an option in the OC bootloader.

Do I need to add something to the macOS EFI partition to boot Windows (I have a backup of the Windows EFI if that's handy)? Do I need to somehow create an EFI partition on the Windows drive (presumably this is what it would have done if I disconnected the nvme drive before installing Windows, but that'd be a pain)?

Also, would appreciate a little clarification on the Dortania multiboot guide. Am I correct to assume Bootstrap.efi is just to prevent Windows from overwriting the macOS EFI (fwiw I already set that up)? And that Bootcamp is an option for multiboot, but it's not required? Ideally I'd just like to select Windows from the OC bootloader and it just think it's a normal PC rather than Windows running on Mac hardware.

edit: upon further reading it sounds like maybe I don't want to boot windows from OC. So I have the same question but just want to boot to macOS by default, but have option to boot windows from BIOS (which seems like later I could convert to rEFInd).

Thanks,