Monterey upgrade refuses to install
QThe Monterey upgrade refused to install on my iMac 2017 27-inch, telling me that I had to turn off FileVault. When I did that, nothing happened. Why can’t it upgrade?
ABecause of differences from older versions, upgrading to Big Sur or Monterey can cause problems, and you may be asked to turn off FileVault first. When you do that, the volume isn’t necessarily decrypted immediately. The process can take a long time, so you should leave your Mac running and awake for a day or two before assuming that it won’t decrypt.
If that won’t work, the best approach is to ensure that you have at least one, preferably two, complete and recent backups, then start up in Recovery, format the drive, and install Monterey afresh. During that, opt to migrate from your backup, and at the end you’ll have a clean install with your old files migrated.
Other options worth considering include starting your Mac up in Safe mode and letting Software Update upgrade it there; this is a recognised use for Safe mode, although it won’t work around the problem posed by FileVault encryption. Sometimes it’s simpler to make yourself a bootable external installer disk, restart from that, and run the upgrade from there. Apple’s instructions are at apple. co/3uGwAfP. Before trying that on a Mac with a T2 chip, you’ll need to visit Recovery to allow it to boot from an external drive.
Although most prefer to migrate during the upgrade, there’s no reason you can’t delay and use Migration Assistant later.