Migrating from High Sierra to Catalina -- lost files/photos

[mad cow disease]

Old MBP running High Sierra. Will no longer boot -- it's the 2011 GPU issue. New computer is a MBA running Catalina. Part of the problem, I think, is that the MBA has a 256 GB SSD and the old one had a 500 GB HDD.

Two issues:
1) Tried to migrate from a old Time Machine backup about a week before the old MBP died, and after migration the photos app couldn't locate the old photo library and asked to "select a library." The library in the photos folder seems to be an old file, about six years' worth of photos is missing. This person was merging their iPhone/iPad photo libraries manually by connecting to the photos app every time. Any ideas on how to locate it? Have already searched for files using the ".photoslibrary" suffix. No dice, and I can't search the Time Machine volume for some reason.

2) Also couldn't migrate the Music folder either because of the HD, we created space on the new SSD for the music folder, but now can't migrate that using Migration Assistant, either. Nor can we restore from a Time Machine backup (those backup files are inaccessible in Time Machine).

I can't believe how poor this experience moving to the new computer has been. About ready to throw in the towel. Any suggestions? At this point I am considering cracking open the old MBP, installing the HDD in an enclosure and booting up from it, but can I even do that on USB 3.0 through a USB-C adapter?

 

[velocityg4]

The OS on the old computer likely is too old for the new one to boot. You can still hook up the old drive in the enclosure and move the files manually.

Sometimes migration fails. So it's best just to do it manually. If the files aren't where they should be after migration. They probably aren't there. I'd just focus on the next step of connecting the old drive.

 

[brianmowrey]

Definitely abandon ship on TM and retrieve the HD. You won't even need an enclosure, just a SATA-USB adapter (either USB-C or USB-A that you plug into dongle). Then just check your Mac's security settings and you're good to go! ...except for the OS being incompatible.

You will want to clone the drive to another external as a backup first thing. Then you can safely use the MBA Recovery Mode to install Catalina on it, which will let you boot the MBA to it. Alternately, find a friend with an older Mac to boot into the drive without updating the OS.