Bootcamp install messed up partition or ???

I only ever used Windows Bootcamp once for a short time decades ago so I don't recall how Windows treated the system. In your picture of Windows Disk Management screen, just because it shows the macOS partition as healthy doesn't mean Windows can use it in any way except to reformat it because it doesn't show its file system or assign it a drive letter.

How did you create that original 750GB partition you intended to use for Windows? Did you first install macOS to the whole physical SSD so there was just a single partition (aka APFS Container) for macOS....then used Bootcamp Assistant to resize the partition to create the Windows partition?

FYI, to get a true look at the drive layout you need to use the command line in macOS since Disk Utility will hide things from the user....it appears Windows may be doing the same in Disk Management as well, but macOS is showing the missing storage as being part of macOS which is weird. Here is the macOS command to see the layout of the internal drive:

diskutil  list  internal

macOS is finicky when trying to remove Windows & reclaim the storage used by other operating systems. You can try using Bootcamp Assistant to remove Windows which should delete the Windows partition and merge it back into the partition from which it was split. Unfortunately some people find that these other partitions don't always merge back into one another and back into the macOS Container. It is possible to merge those partitions back using the command line. I posted some instructions in another post here (may need to be modified a bit for your case since I wrote those for two specific cases, but there should be enough information there to figure it out if modifications are needed for your case), otherwise it may be easier to just start over with a clean install of macOS on the whole physical SSD (Doesn't hurt to experiment here since you have no data on either partition):

Merge (free space) item back into APFS Container -- HWTech - Apple Community

Merging multiple partitions back into APFS Container -- HWTech - Apple Community

Did you deactivate Windows in your previous installation before wiping it? I suspect MS still thinks it is in use. You should be able to log into your account on microsoft.com and check your installations there - and removing the activation belonging to your previous installation should free the license for reassignment.

You sure that Apple isn't reporting the drive sizes in Base10 and Windows in Base2? 1 TB = 931 TiB, so the numbers look about right to me - no missing space at all.