git-annex's handling of an external special remote that sends VERSION 2 is not stellar currently:

joey@darkstar:~/tmp/b>git-annex initremote t type=external externaltype=test encryption=none 
initremote t 
  external special remote protocol error, unexpectedly received "CONFIG directory store data here" (command not allowed at this time)

git-annex: unable to use special remote due to protocol error

joey@darkstar:~/tmp/b>git-annex copy --to t

  external special remote protocol error, unexpectedly received "UNSUPPORTED-REQUEST" (command not allowed at this time)

  external special remote protocol error, unexpectedly received "UNSUPPORTED-REQUEST" (command not allowed at this time)
copy x 
  external special remote protocol error, unexpectedly received "UNSUPPORTED-REQUEST" (command not allowed at this time)
(unable to use special remote due to protocol error) failed
copy: 1 failed

Protocol debug shows what's happening:

[2023-03-28 16:00:09.361602472] (Annex.ExternalAddonProcess) /home/joey/bin/git-annex-remote-test[3] --> VERSION 2
[2023-03-28 16:00:09.361764519] (Annex.ExternalAddonProcess) /home/joey/bin/git-annex-remote-test[3] <-- ERROR unsupported VERSION
[2023-03-28 16:00:09.361897595] (Annex.ExternalAddonProcess) /home/joey/bin/git-annex-remote-test[3] <-- EXTENSIONS INFO GETGITREMOTENAME ASYNC
[2023-03-28 16:00:09.362112912] (Annex.ExternalAddonProcess) /home/joey/bin/git-annex-remote-test[3] --> UNSUPPORTED-REQUEST
[2023-03-28 16:00:09.362212948] (Annex.ExternalAddonProcess) /home/joey/bin/git-annex-remote-test[3] <-- PREPARE
[2023-03-28 16:00:09.362332494] (Annex.ExternalAddonProcess) /home/joey/bin/git-annex-remote-test[3] --> UNSUPPORTED-REQUEST