mart wrote:

What would be more effective: Another layer of dryall and green glue or
acousti-seal on 1 side or filling the wall with cellulose? Studs are NOT
offset.

The likely most effective solution is screwing horizontal metal
acoustical channels to the existing studs and screwing another layer
of drywall to those strips, first making sure to seal all air leaks,
including any around wall outlets (you don't want any one stud cavity
to have outlets for adjacent rooms). This actually gives a higher
acoustical STC rating than a wall made with offset studs. Just
adding another layer of drywall won't help much. I probably wouldn't
use cellulose because it's messy, compared to fiberglass batt.