After Restore: An operating system wasn’t found...

I have a Lenovo e560 with 500GB SSD drive, running Windows 10 v20H2. Although I have Acronis True Image 2021, I am using v2020 build 38530, (for reasons explained elsewhere, this has had to be ditched.) The hdd is formatted as MBR (BIOS is set to boot from both UEFI and Legacy) and NTFS, with 3 partitions,: C: 165.2; Hidden 558MB and D: 300GB. (These may not be the exact sizes of the partitions the backup was made, but are far larger than the content. C: is roughly 50% used for Windows 10 and D: roughly 30% for file storage. With my back ups, I back up the C drive on the 1st of every month and D just occasionally; both True Images as full backups to my NAS.

Last week I tried reinstalling Windows 10 because of an occasional problem. Not getting very far, I decided to go back to my most recent backup tibx files. Each time I try and recover my C drive, (D can wait) on reboot I get the message that an operating system wasn’t found.

I have the ‘Rescue Media Builder’ on a USB memory stick and I moved the .tibx file from my NAS to a 2TB USB drive.

After recovering my C drive, by mounting the drive on another laptop via a SATA interface, I can see that my C drive is at it would have been at the last backup (1 April 2021) in terms of the file dates, etc. For some reason the system is not being seen or accepted.

Any suggestions, please? What I am doing seems to be exactly what True Image is meant to do, and has done for me over many years.