What Colif didn't mention is that Windows 10 is unlike other prior versions. This particular version is as bad as Apple products, it wants to hog everything, claim everything unto itself.
That means when installing windows, it's seriously advised to physically unplug All other drives, or windows will treat all the drives as if they are C: . C:/ssd could very well be the boot drive, but the information and files might be stored on d:/hdd, and at boot c: pulls the info from D: into c:/cache and then proceeds to boot.
It's a cra*tastic way to do things, but the W10 library system makes it happen that way. Just as Steam main files are under C:/program files (x86) yet my entire library collection is on D:/steam apps, yet any in game snapshots go to D:/photos.
I have 1 nvme. No other drives. Just 1 physical drive for everything. Windows install setup 3 partitions. 3. 500Mb is listed as B: volume #0, that's the rescue CAB files etc. Volume #1 is C, and volume #2 is non-lettered 100Mb that contains All the boot info except for what's contained within Windows. It's the GPT info, or in some cases the MBR info. There's nothing saying that the actual boot info must be in that particular partition, if I had multiple drives, it's entirely possible the addressing is in fact on a physically seperate drive, libraried there by the windows install.
Win10 is best installed first, complete with updates and all other Windows necessities. Once fully installed, only then plug the data cables for the other drives and download Steam or whatever games or other media installs etc. Windows will then treat the other drives as seperate entities, additional storage, not as part of Windows storage itself.
I'd start with ccleaner, clean up all temp files and associated stuff. Run malwarebytes and then anti-virus, they are 2 different things. Then run the ccleaner registry tool in default (say Yes to backup). That'll take care of cleaning out orphans and conflicting/dead end addresses from the boot procedure. Then run ccleaner again.
That'll start you out with a clean/healthy windows boot, then see what happens.