Apple’s Logic Remote has some features that might allow midi notes to be sent and the ability to make custom sliders. Furthermore and perhaps more promisingly Apple’s Mainstage app may be the ultimate midi puppet control constructor. Users that already own professional music production software may find they already have a very robust suite of customizable midi controls functionality.

You can also use the STREAMDECK app, it's a low monthly payment. I use it in addition to the STREAMDECK XL when I need additional buttons for triggers (which you can never get enough of. Works with iPad, iPhone, Android devices.

Cool, Dan! THanks for your reply.
I checked out these Apps in the App Store.
Maybe I give them a try, but they are quite expensive for only playing around.
Looking forward to Metagrid 2.0 coming :)
Q: Can you do sliders as well? Or is it limited to buttons?

I tried an additional setting: I just dragged my whole Controls panel on the connected iPad Pro 12" (via Luna Dongle) and maximized the panel. In this way I can use the picture buttons of CH.
Works quite well and you have it directly named by CH an everything.

I've actually experimented a bit with this.

I've used Lemur, TouchOSC, and Metagrid on the iPad to send MIDI notes and CC values to CH from the iPad. It works wireless or wired. These applications are very fully featured so you can set up different templates that are easily switchable. It's quite slick.

None of the above apps let you make custom pictures for your buttons, but Metagrid said it would be in the 2.0 update. I was waiting for that update before making a tutorial video on how to do it, but could probably find time to make one before then.