There will be more changes coming for Beta release. That I know of will be kernel 5.4.x and Qt 5.14 RC or Final plus the usual many updates package versions.
Don’t know what you mean. OpenMandriva like most Linux distros uses dynamic configuration for display drivers so what ever display driver it uses depends on the graphic hardware. Needless to say this applies to opensource display drivers. We don’t have real support for proprietary graphic drivers.
So I guess the display driver default would be what ever the operating system thinks your graphic hardware is supposed to need.
So on my Ryzen5 box I have Radeon R7 240 GPU so system uses radeon driver by default. I can add kernel parameters to get it to use amdgpu driver if I so choose. (Yeah, FWIW that is a very cheap, low end, GPU.)