For this particular problem, you can’t compare the iPhone w/your MacBook. The iPhone does not update from Zwift servers, instead downloading from Apple servers. Also, the updates for your phone app or not just updates (i.e.,subset of changes or a patch) but instead the whole app w/changes. With your MacBook, it’s downloading a patch or partial set of changed files.
The reason I suggested using your iPhones hotspot to connect your laptop or connecting via VPN, is that it is possible that there is a cache issue on the the local Zwift CDN that your computer is trying to download the update from. By going to mobile data or VPN, you could get connected to a different CDN and successfully complete your download/update.