what will be the best or next best table top computer for FS 2020? Eventually I may run 4 mointers and want to have smooth running scenery maxed out
I don't think you can buy a machine that will run it today.
They usually build the Sim to last a while so the top machine today will run it well but not run it full out.Here are the Microsoft Flight Simulator 2020 System Requirements (Minimum)
Microsoft Flight Simulator 2020 Recommended Requirements
You might want to read this.