I think a big three team trade is needed to move Simmons and possibly Harris too in a blockbuster trade. Something like this (could not be completed until Jan 15)
Sixers get: Tyler Haliburton, Buddy Hield, John Collins, Cam Reddish, Deion Wright, Kings 2022 1st round pick
Kings get: Ben Simmons, Hawks 2022 1st round pick (via Thunder)
Hawks get: Tobias Harris, Matisse Thybulle, Shake Milton, Damian Jones, Sixers 2023 1st round pick.
Sixers get an up and coming PG with Haliburton who shoots the three well, more shooting with Hield, a power forward to replace Harris in Collins, plus good depth with Reddish and Wright, plus a better 2022 1st than their pick will be. Wright could also be flipped for some 2022 2nd rounders, which the Sixers lack.
Kings get Simmons, potentially the best player in the trade, plus a 1st round pick in the 2022 draft to replace the one they send to the Sixers..
Hawks get Harris, a PF to replace the disgruntled Collins. a young center in Jones and a plus defender in Thybulle, depth with Milton and a 2023 1st from the Sixers (the price for the extra salary of Harris).