Something seems to have changed recently. I know it didn't used to do this.
Opus 12.22 x64 on Windows 10 pro.
In a local folder under my users folder, whenever I try to delete or move a file it prompts for UAC. This does not happen with file explorer, only Opus. All file permissions and attributes appear correct.
If the permissions don't block Explorer then either the files are (temporarily) in use -- which can happen while thumbnails or other metadata are being obtained for them in some cases -- or something else is blocking the action with an access denied error.
Windows Defender has been causing people a lot of problems lately, including with documents folders, and will block some actions by some programs (and not others) without informing you that it has done so. If you're using Defender, try whitelisting dopus.exe in all the different parts of it (antivirus scanner, protected folders, privacy guard, etc.).