I met the same issue, it will only happen when you trying to freshly install wow on a M1 macbook. The reason seems to be the indices folder under Data folder.
So the solution is copy a WoW folder from other place, even windows version is okay, and you can delete other files just keep the indices folder and it’s files with its parents folders, about 500MB, and locate the game in Battle.net app, the update will start without problem.
I don’t have an EU fourm account so I post the solution here, hope it will help someone.
This is the only solution that has worked for me. Thank you so much for sharing!
Notes for those who are trying to troubleshoot:
I’m installing on an external harddrive because my Macbook doesn’t have a lot of space
I tried every possible work around listed (including the use of WoW Classic files to “trick” the client into leaving the update loop) with no success
I have a windows installation of WoW and grabbed the indices folder only (and everything inside) and replaced the indices folder in my broken WoW installation.
I’m finally at the actual download of the game - yay! - it allowed me to get out of the dreaded update loop.
I’m still in the process of downloading, if something goes sideways I’ll update. Otherwise, you can consider mine a success!
FWIW, what worked for me was installing World of Warcraft (https://download.battle.net/en-us/?platform=macos&locale=en_US&product=wow) rather than Battle.net. They both end up installing Battle.net, but for some reason, when I tried to use the Battle.net installer, even the installer was incredibly slow, and then I encountered all the issues referenced in that thread (bnet launching multiple “agent” processes that each went crazy and got nowhere).
But using the WoW installer directly had none of these problems. The only issue I had was the first attempt by Bnet to install WoW grinded to a halt. I just changed the settings to remove bandwidth caps, then paused and re-started the download. Worked great.