Just found the same problem, I was getting permission denied when I tried to connect from my laptop to my iMac shared folders
My setup:
iMac 2020 27", Big Sur 11.1
Macbook Air 2015, Big Sur 11.1
I entered those two commands from this thread
/usr/bin/kmutil load -p /System/Library/Extensions/smbfs.kext
sudo kextload /System/Library/Extensions/smbfs.kext
And now it's working and can connect from my mac air to the sharing folders in my iMac.
Thank you for the solution.