I haven't tossed out any random trade ideas in a long time but this seems like it makes sense for all the teams involved.
Celtics get Harrison Barnes
Celtics give up Schroeder, Richardson, Hernangomez, and a lotto protected 1st
Kings get Ben Simmons and Josh Richardson
Kings give up Fox and Barnes
76ers get Fox, Hernengomez, Cs 2022 lotto protected pick, Jazz 2021 1st
76ers give up Simmons
Jazz get Schroeder
Jazz give up 2023 1st (use their TPE)
My logic
Celtics, they add a playoff proven vet in Barnes who could come in and start pushing either AL or R-Will to the bench. He would give the Cs a clear 3rd option on offense and hopefully stabilize the team. This trade also cleans up the rotation. Moving Schroeder clears the path for a full time role for Pritchard. Moving AL or R-Will to the bench will cut down on the need to play a two big lineup and gives the Cs a relatively clear 8 man rotation with Al/R- Will, Grant and Pritchard being the first 3 off the bench. The open roster spots will allow the Cs to offer min contracts to two on the many guys floating in and out of the league on 10 days deals. (its also likely that the Kings or 76ers would add a cheap player on their bench to make roster space work)
76ers, they move on from Simmons while adding a flawed "star" in Fox and 2 firsts. Not a great haul but one that I think will be in line with his market value.
King, this trade gives them an interesting lineup. Haliburton, Hield, Richardson, Simmons and Holmes is a nice fitting starting 5 with Mitchell as their 6th man. This group is young and the pieces compliment Simmons really well.
Jazz, they are in the Championship push and giving up a late first for a spark off the bench just makes sense.