Windows Defender is not great in our recent experience, FWIW.
We don't have any similar reports so far. (DeleteFile failed; code 5. Access is defined. docsf32.ocx is the only other installer issue/thread currently, but that's about a file that can't be replaced, while your issue seems to be that the files are deleted or reverted after the installer writes them.)
You could try using the installer that is for Windows XP, which uses the old installation method. It's linked in Directory Opus 12.20