iCloud account login no longer functioning with macOS 26.1

[JC-000]

With UTM 4.7.4 I updated a VM to macOS 26.1 from 26.0.1, with the host running 26.0.1, after which I noticed that iMessage was no longer logged in, but it appeared logged into iCloud in system settings. Attempting to log in to iMessage separately threw an "unknown error". I decided to try logging out and back into iCloud in system settings and the process hung. I rebooted the VM and tried again and the workflow functioned normally, but login fails with "could not communicate with server".

I tried updating the host to 26.1 with no effect.

If I look at the VM now I notice that the serial number inside the VM is now blank instead of a pseudo-serial number.

Hardware is an M4 Mac mini with the 10 core CPU and 32GB of RAM.

[JC-000]

I have since replicated this on additional hosts and VMs and some older versions of UTM.

[ANGRYCONE]

delete the VM and remake it

[pingu-the-penguin]

Upstream issue with macOS 26.1.