I've been looking at current digital audio interface boxes to connect guitars and mics to the 2018 released iPad Pros with a USB C connector, and with a headphone jack so you can listen with wired headphones/externally powered speakers (or monitors).
I have found a couple of "soon to be released" products, such as Audient's EVO 4 and EVO 8, and IK Multimedia's iRig Pro Duo I/O, just to name a couple at the lower-cost end of the market, which *may* have iPad Pro 3rd generation support. I have not seen any release dates for these, and I've reached out to the companies to confirm whether they'll support the top end of the iPad lineup. I'll update this post once I've heard back.
I'd like to hear whether anyone else has discovered a product (as of mid-Feb 2020) which connects a guitar and/or mic to the current iPad Pros with a USB C connector, while also providing a 3.5mm or 1/4" wired headphone jack.