i have always the same problem. MacOS BigSur Beta 20A5364e and my RaspberryPi Samba Server didn't connected. VNC and Appache are running well. I have the latest updates from RaspIO 32 Bit and RaspIO 64 Bit.
OK => open terminal tipe su for the root and password
copy -> sudo kextload /System/Library/Extensions/smbfs.kext
and type password.. it runs