On February 11th, 2017 a Southwest's Boeing 737 max-8 made a special flight and wrote the word 'MAX' on sky.
This flight took 8 hours and 54 minutes, it's flew on ground speed about 350kts so on msfs2020 you can make it faster.

All you need is to download the file and extract it to anywhere you want, then open MSFS and go to world map, then click 'LOAD/SAVE' and select the file that you extracted.
I really recommend you to buy download the bredok3d - 737 max for this flight
and the livery of Southwest by slipnoidz from here: https://flightsim.to/file/7724/737-max-southwest

Here is the flight from flightradar24: https://www.flightradar24.com/data/pinned/-c6e57cd#c6e57cd