Sometimes a rock becomes a landscape decoration. This 5'x2' is now one.It looks like leverite to me. (As in "Leave 'er right there".). Just a rock. If it is bothering you, someone might want it for a landscape decoration.
We get that, but didn't you want to find out what kind of rock it is or maybe how it came to be in your yard. Knowing what area it is might give some ideas on what it could be and why its there. And, what's that stuff you're growing...It’s more than an average large rock 🤣
He's going to need to rent one of these, a hydraulic breaker. Shouldn't be too expensive if they work fast and carve out a few feet of the surface of the rock, then they can leave the rest down there.You need to move it for the roots to grow down there.