There's another option you may want to consider.
BEFORE UNDERTAKING THIS PROCESS PLEASE READ THE "CAUTIONARY NOTE" AT THE END OF THIS MESSAGE...
As a general proposition I'm loathe to use a third-party (non-Windows-integrated) program that's designed to make registry changes to the OS. I do so only when I've concluded that utilizing such a program is the only reasonable alternative to achieving a particular objective, and that I'm reasonably assured whatever registry changes are made by the program won't play havoc with my current system and (hopefully) won't adversely affect my system in the future.
I mention this because I'm recommending such a third-party program for your consideration in order to delete the Windows OS from your SECONDARY HDD.
The Windows OS balks at a user's attempt to delete the Windows folder, even when that folder resides on a secondary drive in the system and not on the boot drive. While there are ways for the user to take control of that Windows folder and delete its enormous number of files, the process is quite complicated and generally very frustrating for most users.
A number of years ago someone came up with a simple-to-use program that achieves the objective of deleting the Windows folder (again, we're referring to the Windows OS residing on a SECONDARY drive in the system, NOT the boot drive). It's the "Take Ownership" program - see
https://www.tenforums.com/tutorials/3841-take-ownership-add-context-menu-windows-10-a.html
for a copy of the program. The website's description of the program and its use is quite clear.
As mentioned above, the OS will balk at your effort to delete the Windows (and other OS-related folders) on the secondary drive. Generally a "Folder Access Denied" message will appear when a user attempts to delete that folder, usually with a reference that "...permission from TrustedInstaller..." is necessary to effect any changes to the folder. While it is possible for the user to invoke manual changes in the system that will result in deleting the Windows folder the process is rather complex & tortuous.
The Take Ownership process is an effort to simplify & automate the deletion process for the user. Basically a registry change is made in the OS that will add a "Take Ownership" menu item that appears when you right-click on the Windows folder opening the context menu. After clicking that "Take Ownership" menu item the program will "mark" the nearly 200,000 files in the Windows folders in a manner that allows the user to "take ownership" of them. In so doing, the user can delete all the files/folders in the Windows folder. It's pretty much an automatic process although during this process the user will be asked to confirm the deleting of this or that file. The process is not terribly quick but it's not unduly lengthy and there's very little or no intervention needed from the user during the process. Following the "marking" of the folders/files you can delete the Windows folder. (We usually use Shift-Delete to do so.)
In addition to using the "Take Ownership" registry changes to delete all the files/folders in the Windows folder, you can use the same process for deleting other files/folders on the secondary drive that ordinarily the system would prevent you from doing without going through a rather tortuous manual process alluded to above. Just ensure that before you invoke the "Take Ownership" command from the context menu, you've determined all that data can be deleted without incurring any problems to your system.
Besides deleting the Windows folder, you can also use the Take Ownership process on other folder/files on the secondary drive if need be. Just be cautious about deleting any programs/data that might impact the OS installed on your boot drive. If there's ANY uncertainty, DON'T DELETE the folder and/or files.
CAUTIONARY NOTE...
We've been using this "Take Ownership" program for a number of years going back to Windows 7 and have not experienced any problems or untoward events involving this program. But as I'm sure you know if you've been working with PCs for any length of time, #!)* happens!. That why we ALWAYS recommend that the user FIRST CLONE the contents of the involved HDD/SSD to another drive BEFORE undertaking a major change (such as the one detailed in this message) in the configuration of the HDD/SSD should there's data on the drive the user desires to retain aside from the data the user is deleting by this "Take Ownership" program.
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