Hey FWIW I had the same issue with the crash in the middle of the install (using Mac OS 11.7). I tried 10 different ways to fix it, but the final solution was shutting everything down and restarting the Helix in safe mode (hold down buttons 6 & 12 and turn on the power), then I started Line 6 Updater. The Helix showed up on the devices and I was able to reinstall the update.
Here are some screen shots from the reinstall process that are very important notes as to why the update is crashing on Mac OS: