I physically disconnected all drives to force the EFI partition on the actual Windows drive. It still shat all over boot settings after the first major update.
Someone recommended I try rEFInd and it’s been great. No update has forced me back into the UEFI to set boot order since.
Might be an ASUS MB thing, I never figured it out or bothered afterwards.
I was recommended rEFInd and it’s worked wonders. Never had another boot issue since, and I did like you: physically disconnected all drives except the one I wanted Windows on. Still messed up my boot settings.
Recommend you give it a try if you dare go again.