Strange. If you use File Explorer to make a folder under Program Files, does that trigger a UAC prompt?
As in "Always notify me"? I think the default is the level below that, FWIW, although the difference between the two levels only affects File Explorer and other parts of Windows, not third-party apps like Opus.
Admin Mode won't help there, unfortunately, since it doesn't change how directories are read. It's a rare case where elevating the whole program is needed if you want to look in that directory. (But elevating like that is not recommended in general.)
I sometimes use an elevated command prompt instead, if I'm just trying to get a list of subfolders. (You can then paste the path into Opus and go into the subfolder in a lot of cases. It's only the parent directory that blocks non-admin users from listing the installed applications under it. The applications themselves are readable. It's a very strange choice on Microsoft's part.)
Of course, the real solution to the WindowsApps directory is to avoid installing things via the Microsoft Store. 