Windows install media (either repair partition or install usb stick) had (has?) a nasty bug where it refuses to ALLOW modification of the windows NT bootloader file due to “protect the user from harming the system” mentality, even when booting from repair media. The bootloader as a security measure needs to bless the partition (partition Uuid), it embeds the partition code to the bootloader app, which EasyBCD at the time didnt do. Windows repair failed to do this step not because it couldnt, but due to access priviledges it refused to touch the bootlloader of the drive you’re trying to repair. Search for EasyBCD in the forum history, I have long since forgotten about the the exact details of the drama I had.
I had a similar Ubuntu/Grub based disaster years ago (Adventures installing Haiku to MacBook Pro (11.3, late 2014, on SSD, EFI)). It wont help you solve the problem, but it shows how fickle windows booting is when tools like grub/ubuntu installers corrupt the bootloader or disk partition table. The repair tools of that era failed miserably.
I also had a windows 10 update hose itself on a macbook bootcamp drive. There was a popular dell system used on microsoft campuses, and to fix a dell partitioning issue they had, the windows update accidently corrupted systems with 3 partitions where windows was on the 3rd partition. Even though there weren’t many such cases, lots of people rebooted to a failed update and could never recover into bootcamp windows on partition 3. In my case, Haiku replaced Windows on the macbook pro.
Hopfully the recovery tools in 2024 are better than the tools in 2016 or so.