There are other midi-trigger/key-trigger apps out there that you can customize. The names escape me at the moment, but the moral of the story is you certainly don’t need StreamDeck software to do this type of thing with your phone or iPad. Most of those apps are 1time fee if I recall. Hopefully someone will fill in where my memory fails.
Also, I’d suggest using Duet for anyone with an iPad that would like to do a second display quickly and easily. It’s seamless and easy as could be. Quite literally plug and play once you have the apps installed. This might be a great way to keep the mixer or a different mode open off to the side to minimize switching between modes.