I was looking for a solution that offers functionality like “StreamDeck XL” but without having to buy extra hardware (cause I already own an iPad Pro, which I wanted to use for this purpose.) I found an application called “Touch Portal” (https://www.touch-portal.com/index.php)
It works as expected for me. The company offers a limited free trial version, the full version (Pro) costs only 13,99 € (no subscription).
Just wanted to let you know, cause I had not heard of it before.
Disclaimer: I am not “connected” to the company in any way.