I'm traveling with my family from Faro (Portugal) to Seville (Spain.) It is about a two-hour drive and I found Uber to be one of the most pleasant and reasonably cost-effective ways to travel in Portugal. Is it possible to cross into Spain with an Uber?
I've tested just now and the app returned the options. 191 euros is the cheapiest option. So yes you should be able to request an Uber for this trip.
If you and the driver are citizens of Schengen countries, and/or eligible for the 90/180 rule (and not in violation of it), and the driver is willing, then the answer is yes.
If not, then you'd probably get away with it anyway, but I don't recommend it. The consequences of getting caught can be significant.