HFS / HFS+ / APFS are file systems and should be irrelevant to client systems which connect to a server across the network. A client shouldn't need to know nor care about the details of the server for which it is connecting. All that should matter is the protocol used to connect to the file share. The server software is responsible for the details of accessing files, not the client. Any file server software which requires the client to understand the details of the servers file system is broken.
I'm not sure why are you blaming me for this. It's Apple problem and there is a workaround Apple suggested and had been for awhile. If you read the OP's posting carefully, he can access files on his Mac Pro 5,1 from his older MDD, but not vice versa, because of the way Mojave works with older AFP systems so that's why it couldn't access what's on his older MDD. My Mac Mini is running El-Capitan which "DOES NOT" support APFS; just HFS+ and yet it works on both my Mac Pro 5,1 and all my PowerMac/Powerbooks setup as expected as told by Apple. I think you need to do some learning yourself before you mouth off any blame.
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