Can't start any VMs in Boxes

Recently got a Librem 13v2, and I’m very excited about it.

However, I keep running into problems with Boxes. If I create a new machine from an ISO, it immediately fails to start. This happens with multiple known good ISOs. When invoking Boxes from the command line, I get the following error:

CPU mode 'custom' for x86_64 kvm domain on x86_64 host is not supported by hypervisor

Any idea what may be causing this issue and how to resolve it?

I already opened an issue for this in the PureOS bug tracker; you should add a comment to this bug:

Adding kvm group to your user may help. But in my case still didn’t.