M1 Macs and .iso disk images

I am trying to open an .iso disk image on an M1 MacBook Air that was downloaded from archive.org. It will not open or mount on the desktop. I am only trying to view the contents of this image, I’m not trying to burn a disk, etc. The system error message I get is: “No mountable file systems”. VLC, which always was able to open .iso images previously does not open it either (and I have the latest version). Any ideas?

A “.iso” file isn’t any particular format (despite the name that implies it should be ISO-9660 format), but is a binary image of an optical disc.

That image must contain a file system that macOS understands. Most CD-ROMs today use ISO 9660 and most DVDs and Blu-Ray discs use UDF. Older Mac-specific discs have also used HFS file systems.

I know that Catalina does not support HFS, so any attempt to mount an HFS format optical disc or image of one fails (I’m not sure exactly when Apple dropped this support).

If that ISO image is ISO 9660 or UDF, then I am surprised that it won’t mount, since you almost certainly should be able to mount an actual disc formatted with this format, but maybe Apple dropped this support at some point and I just haven’t learned about it yet.

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Perhaps I’ll contact the source person who lives in Australia to see if he knows why it won’t mount. He very recently uploaded this disk image to archive.org. Obviously, I don’t know if the .iso is a 9660 or a UDF and using “get info” on the icon doesn’t tell me any other details, including what type of .iso it is. Thanks.