I have DO ver. 4. When I connect my Galaxy S21 to my computer I can see the file structure of the files on my phone, but cannot see the individual files. I can see these files using Internet Explorer and or Xplorer2. Does version 12 of DO allow one to see these files?
Opus 4 was an Amiga program, are you sure that's the version you're using? Your forum account says Opus 10.
Opus has supported MTP for a long time, which is usually what Android phones use these days. But there are also (IMO) better options like using (S)FTP to transfer files over wifi, which avoids the drawbacks of MTP (like having to plug a cable in, but also MTP is sometimes not reliable due to bugs in both the Android and Windows MTP stacks which everything depends on).
More advice can be found in the FAQ: