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?
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.