1. First of all, is there any VALID reason why you mention that "a while ago" you installed the OS in a "weird way and probably did all the wrong things" but everything is "fine" now? Of what bearing is all that to your present query?
The reason I raise those questions is that a potential responder to your query wonders could THAT issue the poster mentioned be relevant in some way to the poster's present issue involving (in your case) the deletion of data from a secondary drive in his/her system? Or is it completely irrelevant to the present query?
2. In any event we'll assume you have a perfectly bootable functional drive (SSD) that performs without any problems.
3. Presumably you're going to utilize your HDD for storage/backup and perhaps other purposes so that the Windows OS that's apparently installed on that HDD is unneeded by you. (Of course in the days, weeks, months ahead you're going to ensure that you backup your system comprehensively on a reasonably routine basis so that you will always have a reasonably up-to-date backup of your system, right? You ARE going to do this, right?
4. Apparently there's "stuff" on your secondary HDD - games & such - that you want. But the Windows OS files + related system data on that disk is completely unneeded, right? So since that data takes up a substantial amount of disk-space it's a good idea to get rid of it, right?
5. But it's a pain to navigate through the "normal" deletion of files/folders process. The OS balks at the user's straightforward deletion of data attempts, requiring confirmation after confirmation from the "Trusted Installer" - whoever the hell he/she is. While you can do this manually and spend even tortuous hours doing so, there's an easier way.
6. 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.
Basically the registry change made in the OS will add a "Take Ownership" menu item that appears when you right-click on the Windows folder. After clicking that 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 intervention needed from the user during the process.
(As a general proposition I'm loathe to use a third-party (non-Windows-integrated) program to achieve an objective involving the Windows OS. I do so only when I've concluded that utilizing such a program is the only reasonable alternative in achieving the 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.)
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 we all know when it comes to PCs, #!)* happens!. That why we ALWAYS recommend that the user FIRST CLONE the contents of the HDD to another drive BEFORE undertaking a major change (such as this one) in the configuration of the HDD involved when there's data on the drive the user desires to retain aside from the data the user is deleting by this "Take Ownership" program.