If it works with legacy Input + StandaloneInputModule but it doesn’t work with Input System + InputSystemUIInputModule, then it’s probably a problem with Input System itself. Both components are supposed to send the same events through the EventSystem, which UI Toolkit picks up on. Are you sure you’re using the right options for your specific setup in terms of Pointer Behavior on your InputSystemUIInputModule? I assume it worked well for UGUI before you started translating your content. Does it still work if you add a UGUI button to your scene and try to tap on it with touch input?
In terms of Player settings, are you setting “active input handling” to “Input System Package (New)”? We’ve seen some problems in the past if you set it to “Both” but are intending to use UI Toolkit with the new Input System. If you’re not using “Input System Package (New)”, changing to that might solve your problem.