I think there is a misconception on how palm rejection is working.
On iPad it’s not something you can disable as it’s really built in iOS. It relies on how big the contact surface area is and simply discards the input if it’s bigger than a certain size.
And the one for Apple is definitely good.
I simply can’t interact with the palm when I try.
And it’s not something apps can bypass.
We can simply make it more aggressive by reducing the size threshold, although it’s very bad practice to do that by default (a threshold too low and you can’t interact with it anymore, that’s why Procreate moved the option in the iOS settings instead of inside the app)
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Also in Nomad you should probably hide the toolbox (interface menu). The only reason it’s displayed by default is for feature discovery.
For left-handed, you can swap the UI as well.
That way you have no buttons under your palm.