good catch, thank you.

if you look at the actual report summary however it shows that they want to change that:

https://digital-strategy.ec.europa.eu/en/news/commission-pub...

so even if not a reality in all sectors, removing geoblocking is in the interest of the EU.

going back to the original question:

Why should other EU members care what websites Spain allows their citizens to access? Does the "EU" even have authority for such a thing?

they do care, and they should, and yes, they have the authority.

personally, when i read the report, seeing how young people are more interested in viewing content from other countries, what first came to my mind is the increased integration of EU countries and cultures that comes from that. that's the why.