I'm thinking that perhaps your current installation was done with legacy BIOS settings and consequently is legacy MBR and does not have the expected Windows Boot Manager schema required for UEFI, GPT, secure boot, etc.
Just my best guess.
You might start your research there by querying the disk to determine if it's GPT or MBR.
Have you purchased a new hard drive but cannot access all of its disk space? Luckily for you, this article will teach you how to convert MBR to GPT.
adamtheautomator.com
IF you find that, that is the case your best bet would likely be to back up your critical data and start over with the proper BIOS configuration.
There are tools that promise to do the conversion without damage to existing data, but....
I have no experience in using them and as such can not make any recommendations.
In any case a reliable backup including perhaps a disk image will give you some peace of mind going forward.