Audio format output form lightning port of iPad pro 2017 10.5 inch

It should be the AAC (Advanced Audio Codec) standard format.

If you're referring specifically to Apple Music, see also this support article about ALAC (Apple Lossless Audio Codec):--> About lossless audio in Apple Music - Apple Support

Regards

Giulio

If your device has a Lightning port, According to Apple’s specs, your device supports MP3, AAC, ALAC, WAV and AIFF audio files - and FLAC files with an appropriate App.

The audio stream from the Lightning port is limited to 24-bit/192kHz when using an external DAC. Internal DACs, where fitted, are limited to 24-bit/48kHz sample rate.

You are very welcome.

My pleasure