Control or disable overlay blocking keyboard?

If the overlay appears when you tap a text field or start typing, I’d check Settings > Accessibility > Hover Text > Hover Typing.

You can turn Hover Typing off there. If you want to keep it, you can also change its Display Mode so it doesn’t sit above the onscreen keyboard.

If that’s not the overlay you’re seeing, a screenshot or a brief description of what appears on the screen would help narrow it down.

Please post a screenshot - as with a better understanding of precisely what it is that you see, contributors here may be better able to offer appropriate help or guidance:

Take a screenshot on iPad - Apple Support

You can post your screenshot (redacted as necessary, using markup tools, to obscure any personal or sensitive information) using the image button located at the bottom of the message editing window: