AMD Graphics not detected

I would recommend first of all to not install the drivers coming from outside the distribution unless you really know that you need them. Ubuntu 18.04 is pretty new and the open source drivers for AMD are in great shape.

The situation is not so great for multi-gpu configurations though. But if you just want to use the AMD graphics card instead of the Intel one, there is usually a workaround that works pretty well.

In your laptop BIOS, you usually can choose which one will be the default active graphics card. You should choose there the AMD one. That will be the main GPU from now on and it will be the used by Linux.

Since it seems that you have issues with your graphical environment, I would reinstall the distribution from scratch if you don't know how to perform a cleanup of the drivers that you installed separately.