Cannot merge back space left by bootcamp
You want to grow the APFS container, not the physical drive that it's on (as this would be impossible, obviously). This can't be disk0, and it looks like it's disk1 in your screenshots, so diskutil ap resizeContainer disk0s1 0 should do what you want. 

There is no disk0s2 to operate on, so that should error based on your excellent details in the question.

It’s safe to do a live resize of the container.