I’ve been working on legato 2-handed block chords. The basic theory is that your right hand plays the melody note with the 5th finger, and voices 3 notes beneath. Then the left hand plays the same note as the fifth finger of the right hand. So the melody note is doubled in an octave, while the right hand plays three harmonizing notes between.
The left hand is always legato. This often requires finger substitution. Then the right hand is as legato as possible. The legato technique from my pipe organ textbook was extremely helpful in figuring out how to accomplish this.
It takes a lot of practice.