You won't be able to connect to a shared drive using AFP anymore, if you get the new file system APFS when you upgrade. Apparently you only get APFS if you have a pure SSD drive (not Fusion).
APFS and file sharing
- Volumes formatted as APFS can't offer share points over the network using AFP.
- APFS supports SMB and NFS, with the option to enforce only SMB-encrypted share points.
So I read the note you quoted as "an APFS filesystem can't be exported over the network via AFP", but what you wrote seems to say "a machine running the APFS filesystem cannot mount an AFP exported filesystem".
I don't think your conclusion is supported by the snippet you quoted.
https://support.apple.com/en-gb/HT208018