As for the route you filed:
What you did here was essentially filing the ARNEM3N, but not actually filing it. You filed all the waypoints on the SID instead of the actual SID. Your flight plan must begin with a valid initial waypoint (like ARNEM, in this case), and in some cases you also file your planned SID (I’m not sure whether this is the case in the Netherlands, but you will get something assigned by Delivery anyways which may or may not be the one you filed, so if you’re unsure, it can’t hurt to simply file it). Keep in mind that initial waypoints, individual SIDs, etc. may or may not come with their own restrictions, but in the case of ARNEM3N, there is a mandatory initial route continuation. Sarstedt VOR is also not something you’d file into EDDV, you’d file to one of the STAR starting points (Nienburg VOR is such a waypoint, e.g.) and again, potentially file the STAR as well (in this case I can help you with an answer for this specific case: you always file your planned STAR (and your planned SID) in Germany) at the end. Your route also uses a lot of directs - in general it roughly follows the airways, but all the flight plan checker plugins will most likely complain about such a route and at least in Europe you are usually not allowed to file directs, at least not for parts of your flight that are not in free route airspace.
So, broadly speaking: all of the initial route was incorrect. If you validate that route with Eurocontrol’s validator, you would see that it spits out a couple of ROUTE144 errors, and even if you insert L620 between ARNEM and EXOBA, you get a PROF204 and two ROUTE165 errors; if you try to validate the route you were given by Delivery, though, that will return without errors.
I’d very much like to discourage you from using MSFS’s in-sim flight planner to plan your routes as it is horribly bad. Good options for finding valid routes are the Global Route Database or edi-gla; you can then take those routes to SimBrief to create a flight plan (SimBrief itself also suggests routes, but those can also be quite bad - if you keep an eye out for the ones with the Eurocontrol icon, though, those will usually be fine).
Now, the CJ4 is a very well simulated airplane since the WorkingTitle mod became part of the stock version, and the FMS very accurately simulates most functions of its real world counterpart, so - sure - it might have been a lack of knowledge on your part. You might want to check the (now slightly oudated as it is based on the original WorkingTitle mod and there were some changes since it has become the stock model) WorkingTitle CJ4 User Guide to learn about the FMC.
It may, however, also have been a navdata issue, but I doubt that since MSFS usually updates the AIRAC in somewhat regular intervals, and should be on 2308 right now iirc. Since none of these airways have changed in any way with the current 2309, that shouldn’t have been a problem. While it’s not required, it’s generally a good idea to use up to date nav data on VATSIM (old data might result in problems and delays for you, especially in busy/complex airspace as controllers have to coordinate solutions for you which can take some time); unfortunately, worldwide data is not available for free (I believe the data for the US can be gotten for free from the FAA, but that obviously will remove nav data for all places outside the US), the two options I know of to get up to date nav data are NavDataPro (there’s also a version with LIDO charts for a slightly higher price) and Navigraph (which also has a cheaper subscription that only includes nav data), with Navigraph being the more popular one. But as I say: MSFS updates the nav data relatively regularly itself, so most of the time you shouldn’t have an issue with that.