Some years ago we changed Opus to avoid trying to thumbnail *.tmp files because of Photoshop and similar problems.
From testing with Photoshop (23.5.1) today, it only uses a temp file when saving over an existing file, not when saving a new file. When saving a new file, it writes to the final name directly, without any *.tmp file or rename at the end.
Are you seeing the problem when saving a new file, or when saving over an existing file?
Photoshop is also opening and closing the output file a bizarre number of times, which with a long/slow operation like a large file on a network drive is going to leave the window open for something else (not just Opus) to start looking at the file.
I'm not really sure what we can do about the non-tmp case here that would be reliable and not cause other problems or long delays thumbnailing other files. It's really something Adobe should fix; they shouldn't be releasing their write lock on the file until they've finished writing data to it. If they can't easily avoid that due to how their code is structured, they should at least be retrying when re-opening the file to write more data to it. (Or they can write to a *.tmp file first and then rename it at the end, even when creating a new file, which would solve the issue with Opus but possibly not with all other tools that do thumbnailing and indexing.)
It's possible File Explorer isn't triggering the problem simply because Adobe no longer provide a PSD thumbnailer for the Windows shell, so it isn't trying to thumbnail PSD files in the first place.
Regarding Blender, could you make a Process Monitor log of what happens when you save a file with that? Depending on how the saves are done, we may be able to avoid trying to thumbnail its files.