I'm about to downgrade form High Sierra to Sierra. I used time machine for backup.
Will I be able to recover installed programs using time machine or migration assistant? Or do I have to reinstall everything? I've read that photos and documents etc. are not an issue.
Is there a good guide to use Migration assistant or Time machine for the recover?
I'm booting Sierra OS from external drive.
Thanks,
Fred.
iMac (Retina 4K, 21.5-inch, Late 2015), iOS 10.1.1
Since you use Time Machine, do you not have a backup of its Sierra installation? If you do, that would be easiest.
Here are the instructions for using Migration Assistant: How to move your content to a new Mac - Apple Support. In it, the "new Mac" is the one now running High Sierra. After erasing that drive and installing Sierra, it will ask if you want to transfer your content from another Mac or Time Machine backup. That's what you'll be doing. In fact, you could simply boot from the external drive running Sierra, and use Migration Assistant to transfer the internal drive's User Account. Then, use Disk Utility to restore the external drive to the iMac's internal one. That's another option.
Recover after downgrade
