I've posted this on the discord but will post here as well incase I get the answer here but also to make it a answer for future users here should I get an answer.

I've loaded and completed a flight using the FBW & SimBrief integration. Landed at my destination and now want to return.

Is there a way to load another SimBrief flight plan without exiting to the main screen?

Once you land at your destination, parked your 320 at the gate. You can then start Simbrief (with FS2020 still running) and plan a return flight. Select MCDU Menu, ATSU, AOC MENU, INIT/PRES and INIT DATA REQ. Refuel and off you go.

John