In case anyone else running macOS beta or dev builds runs into the issue where the installer gets stuck on "preparing..." (or gets stuck in general) I wanted to collect known workarounds as well as what finally fixed it for me. In my case, I was on macOS 11.2 beta going to the 11.2 RC from the Apple Developer site. I think some techniques here could work for the release version as well, but YMMV.
First -
- try booting into safe mode and then run software update again, or
- if available, try installing the update from the app store
If that doesn't work:
1. remove the beta profile (System Preferences > Software Update > "Details…")
2. reboot and then reinstall the beta profile from Apple Dev or beta.apple.com
3. check for updates. you should be offered the full ~12GB installer
4. create a USB drive installer from the full download using the createinstallmedia command
5. reboot and hold down option (Intel macs) or the power button (M1 macs) until you see the startup disk selector
6. choose the removable installer you just created
7. run the install from there over top of your existing operating system. There should be zero data loss.
8. boot into your updated operating system and check for software updates again. In my case, I was offered another smaller update that installed properly
I hope this helps someone as I was getting close to the point of wiping and restoring until I figured this out.
First -
- try booting into safe mode and then run software update again, or
- if available, try installing the update from the app store
If that doesn't work:
1. remove the beta profile (System Preferences > Software Update > "Details…")
2. reboot and then reinstall the beta profile from Apple Dev or beta.apple.com
3. check for updates. you should be offered the full ~12GB installer
4. create a USB drive installer from the full download using the createinstallmedia command
5. reboot and hold down option (Intel macs) or the power button (M1 macs) until you see the startup disk selector
6. choose the removable installer you just created
7. run the install from there over top of your existing operating system. There should be zero data loss.
8. boot into your updated operating system and check for software updates again. In my case, I was offered another smaller update that installed properly
I hope this helps someone as I was getting close to the point of wiping and restoring until I figured this out.