This is not true, most GA aircraft are equipped with the required instruments for IFR flight.
This depends on the SID / STAR, you need to review the charts to see if there are altitude and or speed restrictions. If there are, and your aircraft can’t meet them, you cannot fly the procedure.
There are also equipment restrictions “turbojet only” etc…
Charts are your friend.
Scrap the in sim flight planner, use something like Navigraph or Little Nav Map.