It is impossible to guess what happened … but your issue look like - albeit which another origin
→ Since May/June 2025: VirtualBox - cannot create new VMs and add existing VMs
→ Virtualbox: cannot create new VMs nor add existing VMs
I don’t know if your use of an RT kernel is necessary - but if it is - you can get a supported kernel.
I suggest you switch to a supported kernel.
sudo mhwd-kernel -i linux617-rt
Or the LTS version
sudo mhwd-kernel -i linux612-rt