Just by reading the interface recommendations for the new iPhone X, I would say that all the elements (including the bottom tabs) in the full-screen web view are cut off at the edges:
When designing for iPhone X, you need to make sure that the layouts fill the screen and are not hidden using the rounded corners of the device, the sensor housing or indicator to access the main screen.
But just as Apple did for its native UI elements, Ionic is likely to come up with a solution for its interface elements (if necessary).
They also mention that there is already a simulator, so you can try what happens:
Preview your application on iPhone X. You can use Simulator (included with Xcode) to preview your application and check for clipping and other layout problems.
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