Comment 7 for bug 1936894

Pre update
root@h:~# qemu-system-x86_64-microvm -M ? | grep -e 'default' -e 'microvm'
microvm microvm (i386)
pc-i440fx-hirsute Ubuntu 21.04 PC (i440FX + PIIX, 1996) (default)

Upgrade
apt install qemu-system-x86
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
The following additional packages will be installed:
  qemu-block-extra qemu-system-common qemu-system-data qemu-system-gui qemu-utils
Suggested packages:
  samba vde2 debootstrap
The following packages will be upgraded:
  qemu-block-extra qemu-system-common qemu-system-data qemu-system-gui qemu-system-x86 qemu-utils
6 upgraded, 0 newly installed, 0 to remove and 18 not upgraded.
Need to get 12.6 MB of archives.
After this operation, 1024 B disk space will be freed.
Do you want to continue? [Y/n] Y
Get:1 http://archive.ubuntu.com/ubuntu hirsute-proposed/main amd64 qemu-utils amd64 1:5.2+dfsg-9ubuntu3.2 [1262 kB]
Get:2 http://archive.ubuntu.com/ubuntu hirsute-proposed/main amd64 qemu-system-common amd64 1:5.2+dfsg-9ubuntu3.2 [1697 kB]
Get:3 http://archive.ubuntu.com/ubuntu hirsute-proposed/main amd64 qemu-system-gui amd64 1:5.2+dfsg-9ubuntu3.2 [38.3 kB]
Get:4 http://archive.ubuntu.com/ubuntu hirsute-proposed/main amd64 qemu-system-data all 1:5.2+dfsg-9ubuntu3.2 [1109 kB]
Get:5 http://archive.ubuntu.com/ubuntu hirsute-proposed/main amd64 qemu-block-extra amd64 1:5.2+dfsg-9ubuntu3.2 [50.3 kB]
Get:6 http://archive.ubuntu.com/ubuntu hirsute-proposed/main amd64 qemu-system-x86 amd64 1:5.2+dfsg-9ubuntu3.2 [8478 kB]
Fetched 12.6 MB in 2s (7536 kB/s)
(Reading database ... 48802 files and directories currently installed.)
Preparing to unpack .../0-qemu-utils_1%3a5.2+dfsg-9ubuntu3.2_amd64.deb ...
Unpacking qemu-utils (1:5.2+dfsg-9ubuntu3.2) over (1:5.2+dfsg-9ubuntu3.1) ...
Preparing to unpack .../1-qemu-system-common_1%3a5.2+dfsg-9ubuntu3.2_amd64.deb ...
Unpacking qemu-system-common (1:5.2+dfsg-9ubuntu3.2) over (1:5.2+dfsg-9ubuntu3.1) ...
Preparing to unpack .../2-qemu-system-gui_1%3a5.2+dfsg-9ubuntu3.2_amd64.deb ...
Unpacking qemu-system-gui:amd64 (1:5.2+dfsg-9ubuntu3.2) over (1:5.2+dfsg-9ubuntu3.1) ...
Preparing to unpack .../3-qemu-system-data_1%3a5.2+dfsg-9ubuntu3.2_all.deb ...
Unpacking qemu-system-data (1:5.2+dfsg-9ubuntu3.2) over (1:5.2+dfsg-9ubuntu3.1) ...
Preparing to unpack .../4-qemu-block-extra_1%3a5.2+dfsg-9ubuntu3.2_amd64.deb ...
Unpacking qemu-block-extra (1:5.2+dfsg-9ubuntu3.2) over (1:5.2+dfsg-9ubuntu3.1) ...
Preparing to unpack .../5-qemu-system-x86_1%3a5.2+dfsg-9ubuntu3.2_amd64.deb ...
Unpacking qemu-system-x86 (1:5.2+dfsg-9ubuntu3.2) over (1:5.2+dfsg-9ubuntu3.1) ...
Setting up qemu-system-data (1:5.2+dfsg-9ubuntu3.2) ...
Setting up qemu-system-x86 (1:5.2+dfsg-9ubuntu3.2) ...
Setting up qemu-block-extra (1:5.2+dfsg-9ubuntu3.2) ...
Setting up qemu-system-common (1:5.2+dfsg-9ubuntu3.2) ...
Setting up qemu-system-gui:amd64 (1:5.2+dfsg-9ubuntu3.2) ...
Setting up qemu-utils (1:5.2+dfsg-9ubuntu3.2) ...
Processing triggers for hicolor-icon-theme (0.17-2) ...
Processing triggers for man-db (2.9.4-2) ...
Scanning processes...
Scanning candidates...
Restarting services...
 systemctl restart accounts-daemon.service fwupd.service packagekit.service polkit.service rsyslog.service ssh.service systemd-journald.service systemd-machined.service systemd-networkd.service systemd-resolved.service udisks2.service
Service restarts being deferred:
 /etc/needrestart/restart.d/dbus.service
 systemctl restart libvirtd.service
 systemctl restart networkd-dispatcher.service
 systemctl restart systemd-logind.service
 systemctl restart unattended-upgrades.service
No containers need to be restarted.
No user sessions are running outdated binaries.

Post upgrade
root@h:~# qemu-system-x86_64-microvm -M ? | grep -e 'default' -e 'microvm'
microvm microvm (i386) (default)

Works as expected/required now, setting verified