I searched and found an article similar to this one on Microsoft's site:
How to Fix Access Denied Folder/File Errors on Windows 10/8/7

And from my diagnosis I have trouble accessing EFS encrypted files and folders.

'Network Error', 'Windows cannot access... You do not have permission.
I get past that screen, I can see and browse shares but I cannot open encrypted files:

You do not have permission to open this file. See the owner of the file or an administrator to obtain permission.

If I decrypt files I can access them so share or filesystem permissions are not an issue, I can
access the files logged on regularly, I have the key on all Windows logons I use.

I cannot risk security and decrypt the files from my drives. A workaround I have is to run a
Linux VirtualBox install, create a shared folder in VirtualBox of the folders I want to share
that the Linux VM can see, and then setup a Samba server and share the mounted VirtualBox shared
folders. Except for an issue I have with file(s) and/or folders containing dollar $igns, it
works as expected when browsing the Linux shares. I can access files encrypted with EFS, I can
copy files to EFS encrypted folders, they will copy as normal and the file(s) will be in the
folder encrypted. The whole point of EFS is that encryption/decryption should be transparent.

Is this a bug in Windows, or is there something I am missing?

The Linux VM workaround is somewhat useful, except for files and or folders with dollar $igns in
their names, which might be out of scope for this forum, and for systems that are not powerful enough and/or lack RAM to run VirtalMachines...

I am using Windows 10 20H2, but remember this happening on other versions...