If you want just install Mate with a nice dark theming you may try the DarkMate desktop installer: https://github.com/broozar/installDesktopFreeBSD
It is meant for FreeBSD 13.0-Release.
It works on bare metal as well as guest in a virtual machine (I tested it with Virtualbox). You need to follow the instructions given on the Github page (installing it afresh as root in Bios/MBR mode, and adding the user(s) later).
Do you still try to get it running in Gnome Boxes (and/or Qemu+KVM)? I think in that case you will encounter more problems than running it in Virtualbox. By the way, when installing in a virtual machine you do not need to load the amdgpu driver.
It is meant for FreeBSD 13.0-Release.
It works on bare metal as well as guest in a virtual machine (I tested it with Virtualbox). You need to follow the instructions given on the Github page (installing it afresh as root in Bios/MBR mode, and adding the user(s) later).
Do you still try to get it running in Gnome Boxes (and/or Qemu+KVM)? I think in that case you will encounter more problems than running it in Virtualbox. By the way, when installing in a virtual machine you do not need to load the amdgpu driver.