The FreeBSD qcow2 can be used directly without running an install. The one that I used was FreeBSD-13.2-RELEASE-arm64-aarch64.qcow2

For OpenBSD, the installer works after adjusting the devices in the guest.

https://cdn.openbsd.org/pub/OpenBSD/7.3/arm64/install73.img

  - UTM / Create New Virtual Machine / Virtualize / Other
  - Select 'Skip ISO boot' / Continue
  - Hardware / (adjust as needed) Continue
  - Storage / (adjust as needed) Continue
  - Shared Directory / Continue
  - Select 'Open VM Settings' / Save
  - Right-click on Devices/Display and select Remove
  - Devices / New / Serial
  - Drive / New / Import and select install73.img
  - Edit the VM again and move the second VirtIO Drive to the first position by right-clicking on it and selecting 'Move Up'

If you feel inclined, hop on to the UTM Discord and the folks there (me included) should be able to help out.