Hello
I install 6.2 64bit (x86_64/amd64) LXQt in default VirtualBox and receive:
(https://i.imgur.com/HAPbXDx.png)
Are you using the binary from Debian or the binary from Virtualbox? Often less hassle using the binary from Virtualbox. But if you are looking longterm - Qemu/KVM is definitely mature enough to use instead of virtualbox. I did use virtualbox for years.