Welcome.
Your car is equipped with the Audio20 infotainment system, with the optional Garmin Map Pilot navigation on SD-Card.
I don't know if the Garmin Map Pilot navigation software can be configured to show the speed limit for the current road. Others on here might know.
I do know, however, that the Garmin Map Pilot navigation software is the ONLY navigation software that can be uses in the SD-Card slot in the Audio20 infotainment system. No other navigation software can be used in the SD-Card slot.
You could try purchasing the latest version of the Garmin Map Pilot SD-Card, on the odd chance that this feature became available on later versions.
Alternatively, you can check if your car is fitted with the optional Apple CarPlay / Android Auto feature (if not, then it can be retrofited by a specialist), then use any of the many smartphone navigation systems (Waze, Google Maps, Apple Maps, etc) that do display the speed limit for the current road.
Hope this helps.