I have offered blabla rides in the past and have come across 2 requests, both relating to motorcycle parts/accessories! When I looked up on Google, this seems more common than I thought. People who bought fragile items seem to think that Blabla is safer than professional courier company. I turned both requests down merely because I was nowhere near where the pick up/delivery addresses were, they were a good 1.5h detour.
As someone has mentioned here, I could drop a passenger at motorway services or supermarket car park and they can take bus/taxi/another blabla, but not parcel.
So, to answer the OP, you can search the app and if there is a suitable ride, ask the driver.
PS: the other issue is driver reliability. I have had people cancelled their rides with me on the day, because their previous blabla driver has cancelled the journey! And yes, in France and Spain, public transport has appeared to be very limited and too expensive for a lot of people that they have resorted to getting a chain of Blabla rides to travel. So, personally if I was getting a Blabla as passenger, I would only do so if I have no time constraint and not bothered about delays/cancellations.