Comment 0 for bug 1936894

In Focal microvm worked and it was a fine addition for those that wanted to try this approach (mature solution of qemu/kvm reduced for a specific use case) to minimal VMs compared to the new projects (very use-case dedicated, but therefore missing quite some features) that spawned.

But it turns out the configuration to make it a default is broken since qemu 5.2.

Correct (Focal)
root@f:~# qemu-system-x86_64-microvm -M ? | grep -e 'default' -e 'microvm'
microvm microvm (i386) (default)

Broken (Groovy and later)
root@i-kvm:~# qemu-system-x86_64-microvm -M ? | grep -e 'default' -e 'microvm'
microvm microvm (i386)
pc-i440fx-impish Ubuntu 21.10 PC (i440FX + PIIX, 1996) (default)

If you follow the guide
  https://cpaelzer.github.io/blogs/009-microvm-in-ubuntu/
It is still usable and that might explain why - even not being the prime use case - we had zero reports of this so far.
The reason for the latter is that explicitly stating -M microvm (common) overcomes the issue and so do a few combinations with -nodefaults.

Thanks to Michael torkaev for spotting and also fixing this.
But we should backport this as an SRU.