If you look at the very end of the Speccy report on your hard drive it agrees with your estimate of used space. It says 417GB used which is - depending exactly on how this is measured - a pretty good match for your earlier estimate of 403GB.
I also note that if you expand the OS section of the report and look at 'Services, running' you will see that Windows backup is running. What I think is happening - and I may be wrong here because I do not have a great deal of experience with Win 10 - is that your OS is creating a backup of your 'D' drive on your 'D' drive. This would explain the apparent doubling of the used capacity. If you open your file manager and set hidden and system files to 'visible', even if only temporarily, I think you will find a backup file on 'D' of about 203 GB !
Since a backup of a drive on the same drive is of absolutely no value - if the drive fails the backup goes with your data - you might as well delete this file if I am correct and it is there, and get 200+GB back. And you can check to see if the Windows backup service is set to automatic. If it is, change this setting to 'Manual'. If in the future you wish to use the Windows backup system to backup to external storage then you can activate it to do so.
To change this setting press 'Win key + X' then click 'Control panel - Administrative tools - Computer management - Services'. Scroll down the list of services to 'Windows backup' and if it is set to 'Automatic' RIGHT click on it and change the start up type to manual. Then it will only run when you want it to. This should solve the problem.
One further small point :- There is no need to quote everything I, or anyone else, might say in a post as you did above. You will see that everything you quoted is still sitting there immediately above your quote ! By all means use quotes to pick out one particular point from a post, but is almost never necessary to quote a complete post.