What's the deal with singing softly, or singing with lots of volume?

Male singer here.
I'm at a place where I can sing with lots if volume and it sounds fine. I really feel that my support is working great and that I can hit the high notes on pitch.
When I sing softly like ballads or other songs that are more sensetive, my tone is bad. I struggle to hit higher notes, I can't feel my support and im straining my throat.
An example could be Blackbird.
When I sing the startline "Blackbird singing in the dead of night" the word night sounds very forced and I can feel strain in my throat when singing it softly. It's not even that the note is that high, and I can easily sing it when raising the volume and feel my support working.
Is there a way around this?
How do the pro singers do?