It worked fine in Fedora 43, the upgrade probably also upgraded a quemu version and now it seems that the older VM can no longer be started by that:
The gui just says ‘Failed to start “My Vm, my snapshot”’ Button: Troubleshooting Log
That log says:
[...]
<os>
<type arch="x86_64" machine="pc-q35-4.2">hvm</type>
<boot dev="hd"/>
<bootmenu enable="no"/>
</os>
[...]
2026-05-04 09:50:58.137+0000: Domain id=1 is tainted: deprecated-config (machine type 'pc-q35-4.2')
char device redirected to /dev/pts/0 (label charserial0)
2026-05-04T09:50:58.310131Z qemu-system-x86_64: warning: Machine type 'pc-q35-4.2' is deprecated: machines more than 3 years old are subject to deletion after 6 years
2026-05-04T13:01:31.470690Z qemu-system-x86_64: terminating on signal 15 from pid 6380 (<unknown process>)
2026-05-04 13:01:31.685+0000: shutting down, reason=shutdown
2026-05-06 05:35:44.170+0000: starting up libvirt version: 11.6.0, package: 3.fc43 (Fedora Project, 2026-02-16-09:39:43, ), qemu version: 10.1.5qemu-10.1.5-1.fc43, kernel: 6.19.14-200.fc43.x86_64, hostname: David-UB
LC_ALL=C \
[...]
/usr/bin/qemu-system-x86_64 \
-name guest=win10,debug-threads=on \
-S \
-object '{"qom-type":"secret","id":"masterKey0","format":"raw","file":"/home/da/.config/libvirt/qemu/lib/domain-1-win10/master-key.aes"}' \
-machine pc-q35-4.2,usb=off,dump-guest-core=off,memory-backend=pc.ram,hpet=off,acpi=on \
[...]
2026-05-06 05:35:44.171+0000: Domain id=1 is tainted: deprecated-config (machine type 'pc-q35-4.2')
char device redirected to /dev/pts/0 (label charserial0)
2026-05-06T05:35:44.340271Z qemu-system-x86_64: warning: Machine type 'pc-q35-4.2' is deprecated: machines more than 3 years old are subject to deletion after 6 years
2026-05-07T11:15:24.718195Z qemu-system-x86_64: terminating on signal 15 from pid 93637 (<unknown process>)
2026-05-07 11:15:24.937+0000: shutting down, reason=shutdown
------------------------------------------------------------
That is all from before the upgrade to F44.
journalctl --follow shows when trying to run the machine:
May 19 11:06:52 David-UB virtqemud[357548]: unsupported configuration: Emulator '/usr/bin/qemu-system-x86_64' does not support machine type 'pc-q35-4.2'
May 19 11:06:52 David-UB org.gnome.Boxes[356874]: machine.vala:611: Failed to start Microsoft Windows 10, sPlan: Unable to start domain: unsupported configuration: Emulator '/usr/bin/qemu-system-x86_64' does not support machine type 'pc-q35-4.2'
Unfortunately today is the first time I see the warning in the logs, I usually don’t look there as long as everything runs smooth 
Is there a chance to resurrect the machine or should I just scrap it and start from scratch?