SSL is not implemented for named pipe on the server, neither for MariaDB, nor for MySQL.
Therefore SSL settings must be ignored when connecting with named pipe "transport", regardless whether server indicates support for it in its capability flags

Otherwise

C:\work\10.11\xxx\client\Debug\mysqldump.exe  --protocol=pipe -uroot mysql

mysqldump.exe: Got error: 2026: "TLS/SSL error: The message received was unexpected or badly formatted. Error 0x80090326(SEC_E_ILLEGAL_MESSAGE)" when trying to connect

Note, recent versions of server even imply opt_ssl=1, meaning connect with ssl, if server is indicating it. In older versions, [client] section can contain ssl=1 or something else that enables ssl.

Whether the server should indicate SSL support when connection via named pipe, is debatable. The fact is there are versions of the server that do that, or maybe even all old versions do that