greetings @aubrey.wodonga I just tested 4.6.2 and it seems it has not the issue fixed, at least for me:
❯ busctl --user call org.mpris.MediaPlayer2.Plexamp /org/mpris/MediaPlayer2 org.mpris.MediaPlayer2.Player Seek x 100
Call failed: Service error: The service threw an error.
TypeError: p.toNumber is not a function
at F.value (/tmp/.mount_PlexamEbwaw7/resources/app.asar/main.js:2:343120)
at handleMessage (/tmp/.mount_PlexamEbwaw7/resources/app.asar/node_modules/dbus-next/lib/service/handlers.js:305:28)
at handleMessage (/tmp/.mount_PlexamEbwaw7/resources/app.asar/node_modules/dbus-next/lib/bus.js:100:14)
at EventEmitter.<anonymous> (/tmp/.mount_PlexamEbwaw7/resources/app.asar/node_modules/dbus-next/lib/bus.js:110:9)
at EventEmitter.emit (node:events:526:28)
at /tmp/.mount_PlexamEbwaw7/resources/app.asar/node_modules/dbus-next/lib/connection.js:102:14
at Socket.<anonymous> (/tmp/.mount_PlexamEbwaw7/resources/app.asar/node_modules/dbus-next/lib/message.js:55:9)
at Socket.emit (node:events:526:28)
at emitReadable_ (node:internal/streams/readable:578:12)
at processTicksAndRejections (node:internal/process/task_queues:82:21)