I made some small progress on this following my reply.
To recap:
I had an upgrade to Sequoia flagged for my M1 MacBook Pro, which was running Ventura.
In the list of other upgrade items, the Sonoma upgrade was listed (as well as Safari).
I ran the Safari then the Sonoma upgrade, and it appeared to work.
I rebooted, then ran the Sequoia upgrade, which was the only upgrade now available.
This appeared to work, but once I logged in I received an error message. I opened the associated text file:
panic(cpu 0 caller 0x0): t6000dart 0xfffffdf034198d70 (dart-dispext0): Can't ignore lock validation @t6000dart.c:437
Debugger message: panic
Memory ID: 0x6
OS release type: Not set yet
OS version: Not set yet
Kernel version: Darwin Kernel Version 24.4.0: Wed Mar 19 21:16:34 PDT 2025; root:xnu-11417.101.15~1/RELEASE_ARM64_T6000
etc.
I read the comments on Apple community and other support sites, and worked through the suggested solutions:
I rebooted and switched off “Find My Mac” and tried again.
This failed the same way.
I rebooted into Safe Mode, and tried the upgrade again in Safe Mode.
This failed the same way.
I noticed that the Mac wasn’t running Sonoma, but had rolled back to Ventura.
I rebooted and logged in using a blank account (I call “admin"), which is not connected to an Apple ID, and ran the upgrade to Sequoia again (the Sonoma upgrade no longer there).
This failed the same way.
I contacted Apple support.
I rebooted and logged back in as myself, and tried reinstalling the operating system: only Ventura was available.
This worked without problems.
I rebooted and ran the only upgrade now available to me under Upgrades: Sequoia.
This failed the same way.
I rebooted, and went to the app store and downloaded Sonoma from there, and ran the installation.
This worked without problems, and I checked that I was running Sonoma.
I rebooted, and went to the app store and downloaded Sequioa from there, ran the upgrade.
This failed the same way.
Rebooted, checked "Find My" was still turned off, and tried in Safe Mode.
Still failed the same way.
So, I am now on Sonoma, but Sonoma will not upgrade to Sequoia either, with the same error message.
