Let me get this straight. Apple added an accessibility feature that lets users mark buttons with underlines if they want to.
You want a way to defeat this feature, specifically designed to help people with handicaps use their devices, when the feature is something that the user has to ask for.
Why?
It is very likely not possible using standard buttons. If you did figure out a way to do it, Apple would likely reject your app because it defeats a system function meant to help the disabled.
So the answer is: Don't do that.
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