I have the XS Max and I use the Apple camera adapter thingamajingie with my Planck and other custom keyboard (even my Ergodox EZ works). Needs the power adapter lead to be plugged in as well.
The newest iPad Pro seems to work with only a USB-C to lighting cable, probably the port supplies more power. I tried USB-C to lighting cable and it doesn't work, but the above linked adapter works without issues.
It's most likely how the lighting port is configured. I have an iPhone XS Max and my Planck v6.1 doesn't connect via a simple USB-C to lighting cable, I need to use the camera accessory cable thingie and at the same time plugin the power adapter, otherwise it tells me the Planck draws too much power.
The 2020 iPad may actually supply more power via its lighting port so you can power the keyboard comfortably. I've had an iPad on my shopping list for a while now, seems now it makes a lot more sense too :)
For an iPad with an audio jack you just need a a USB adapter for your iPad so you can connect your keyboard.
An official Apple lightning to USB adapter:
A cheaper generic brand adapter:
Either of those should let you send MIDI into the iPad via the usual USB lead you’d use to connect to a computer.
Then you could just use the iPad speakers, or plug some headphones into the audio jack out on the iPad.
I have a Launchkey Mini MK3 hooked up like this and it works nicely.
Of course, but you need the Apple Lightning to USB3 Camera Adapter , an usb hub and an interface.