This applies to All Interfaces

Pro Tools Artist is limited to 32 audio tracks, 32 aux channels, 32 instrument tracks, 64 MIDI tracks, and 16 channels of I/O. This means that in the Pro-Tools Artist I/O, you will be able to see all of your device's inputs, however, only the first 16 inputs will record into Pro Tools Artist, but you can have 32 audio tracks. 

Below is an example of a Clarett 8Pre USB. In Pro Tools, there are 20 audio tracks, however only the first 16 inputs can be used to record audio. 

You would be able to use:

• Analogue Inputs 1-8 
• S/PDIF Inputs 1-2 (9-10)
• ADAT Inputs 1-6 (11-16)
• ADAT inputs 7-8 will not record into Pro Tools Artist