The MCDU uses the same Nav database as the Sim, so yes, the SID from the flightplanner is in the FMS. To be clear: the word ‘random’ refers to ANY SID you choose. LFPG departing RW26 and you want to fly eastward your SID is most likely DIKOL4 or RANUX4 as the transitions are east of the airport and are likely your first enroute waypoints.
You can also just put in the flightplan into the MCDU, turn your Mode selector in the EFIS panel to ‘plan’ and you will see if that’s a SID that makes sense to fly (does it get you to your first enroute waypoint, be careful tho, some SIDs do not have a transition point and MSFS just creates a random route to your waypoint). It’s actually really simple with Airbus, you have to be willing though to spend some time and learn it.
A STAR gets you to an Initial approach fix for a set of runways or a given runway. Say you are arriving from the east you choose a STAR that connects to the last waypoint of your route (transition) that is westbound. Done.
I really encourage you to read through some tutorials that deal with IFR navigation in general. It will really help you understand what you would have to do in order to create a flightplan in MSFS.
It doesn’t make sense for anyone here to guide you through every step of the setup. I have spent some time trying to explain and we are still not past the question why some SIDs/STARs are not in the FMS.
And if you feel like it, you can then get a navigraph subscription and try the same thing with up-to-date AIRAC cylces and such.