For those not wanting to adjust their install, but still would like to see Plasma 5.24 early, a minimal test ISO is uploaded.
Besides Plasma 5.24beta, this ISO also uses the linux-next kernel (5.16.2). This means, you cannot use it in virtualbox at the moment, there are issues running an ISO in virtualbox with any kernel above 5.14.xx (probably AUFS releated).
This ISO also defaults to running a Wayland session, thus no non-free Nvidia drivers are included (non-free is not really ready for Wayland).
Virtualbox does work, just not with the vmsvga option, make sure to set to vboxvga or vboxsvga (no 3d acceleration possible then).