I replaced Emily's 8-9 yo MacBook Air 11" running High Sierra with Apple's latest (M1) Air (Big Sur). A few notes for others who might be facing migrations....
- I used Migration Assistant over WiFi but I didn't migrate any applications. Apps have changed to much, better to install from source. Pay CLOSE ATTENTION when they tell you to write down the user passwords! (I took a photo). Migration Assistant brings over a lot of old junk but it also saves a lot of time; it's a pain to migrate mail archives without it.
- Only 1Password needed Rosetta so far. As I write Office 365 is installing.
- Citrix Workspace for Apple Silicon worked! That was biggest risk.
- I couldn't get Carbon Copy Cloner email notifications working. I contacted vendor. The app works for back up though.
- I didn't want to use the iCloud Document sync feature and Migration Assistant did preserve my High Sierra settings.
- You need to open Photos and let it update before reenabling iCloud photo sync. There's no error message -- it just won't work.
- For multiple users I couldn't update the User Profile Login picture from the user account, I had to do it from my Admin account in Users and Groups preferences. (Needed update for Retina images)
- I did better skipping iCloud setup initially then doing it from each User account separately.
- I had to reenable Fast User Switching on 1-2 accounts.
Overall I ran into a few bugs and glitches but High Sierra is 3 releases from Big Sur so that's a hard jump. Really wasn't terrible so far.
The new Air is rather faster than the 9yo 11" Air, but not amazingly faster than my 5yo MacBook Air (Best Computer Ever Made). Most delays are waiting for servers, so local speedups don't make a ton of difference.
Update 4/2/2021: Alas, it turned into a bit of a disaster.