"Waiting to attach to [app name] on [device name]" message in Xcode

This is because you accidentally selected "Wait for executable to be launched" in your scheme settings.

Click on your scheme to reveal your schemes and scheme settings.

Click on Edit Scheme..., located on the bottom.

Select the Run option on the left and the Info tab on the top.

Within the Launch section, select Automatically and save your settings.

Cause by

Product -> Scheme -> Edit Scheme -> Run -> Info -> Launch automatically