Have you tried looking into the new Input System from Unity. They have some on screen controls:
docs.unity3d.com
The Inventory system has an integration with the new input system, you can download it here:
opsive.com
The documentation for the input can be found here:
The built-in input uses the Input Manager for its input which has mouse, keyboard, and limited controller support. You may install the required Inputs for . . .
opsive.com
I'm sure you can find some video tutorials on YouTube about the new input system on screen controls, using those to pickup items should be fairly straight forward.
I hope that helps