On iPad OS 26, the custom keyboard works correctly with a full keyboard, but with a floating keyboard, there is only one line and the console displays a constraint error.
Unable to simultaneously satisfy constraints. Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. ( "<NSLayoutConstraint:0x600002172c10 V:|-(10)-[TUIKeyboardContentView:0x1039c5410] (active, names: '|':TUIKeyplaneView:0x1039c3e20 )>", "<NSLayoutConstraint:0x600002172c60 V:[TUIKeyboardContentView:0x1039c5410]-(-11)-| (active, names: '|':TUIKeyplaneView:0x1039c3e20 )>", "<NSLayoutConstraint:0x6000021721c0 V:|-(0)-[TUIKeyplaneView:0x1039c3e20] (active, names: UIKeyboardLayoutStar Prev...:0x105160e00, '|':UIKeyboardLayoutStar Prev...:0x105160e00 )>", "<NSLayoutConstraint:0x600002172210 V:[TUIKeyplaneView:0x1039c3e20]-(0)-| (active, names: UIKeyboardLayoutStar Prev...:0x105160e00, '|':UIKeyboardLayoutStar Prev...:0x105160e00 )>", "<NSLayoutConstraint:0x6000021728a0 V:|-(0)-[UIKeyboardLayoutStar Prev...] (active, names: UIKeyboardLayoutStar Prev...:0x105160e00, '|':UIKeyboardImpl:0x109905fa0 )>", "<NSLayoutConstraint:0x6000021728f0 V:[UIKeyboardLayoutStar Prev...]-(0)-| (active, names: UIKeyboardLayoutStar Prev...:0x105160e00, '|':UIKeyboardImpl:0x109905fa0 )>", "<NSLayoutConstraint:0x600002177980 '_UITemporaryLayoutHeight' UIKeyboardImpl:0x109905fa0.height == 0 (active)>", "<NSLayoutConstraint:0x600002172df0 'TUIKeyplane.height' TUIKeyboardContentView:0x1039c5410.height == 217 (active)>" )
Will attempt to recover by breaking constraint <NSLayoutConstraint:0x600002172df0 'TUIKeyplane.height' TUIKeyboardContentView:0x1039c5410.height == 217 (active)>
Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKitCore/UIView.h> may also be helpful.
iPad OS 26 custom keyboard, full keyboard mode is working normally.