Sorry to bump an old thread, but this is disappointing - I was just looking into this to pair with 16" M1 MBP.
Seeing as the larger iPad Pro has the same specs/mini led display as the new M1 MBPs, it's a shame that I can't use one as a colour-accurate 2nd monitor. It appears the resolution is limited to 1080p, 60hz, and no mention of supporting different colour spaces, HDR, or ProMotion.
There's very little excuse for not supporting using the iPad display as a DisplayPort monitor connected via Thunderbolt, it could be added with firmware/os update.