ESA is one of the largest space agencies in the world. There’s nothing opaque about calling it ESA especially in a title. We wouldn’t use initialisms if everything had to be expanded all the time.
Personally I would prefer to call it "Roscosmos/ESA connects..." than "Russia/Europe connects". It adds information for free while keeping it short, just put it in the title. ESA is more specific than Europe or EU, so why make the title more generic and opaque than needed? It tells you it's not a random team of "Europeans", it's not an amateur hacker in the backyard, or some intelligence agency.
The expansion isn't really needed when it's a "household name" in the field. If you read a title about space industry there's no need to expand or explain NASA, ESA, Roscosmos, maybe not even for ISRO or JAXA, although I can see how some of these wouldn't be the most familiar for people in the West even when they have some interest in space news.
"'Miracle': European Space Agency reconnects with lost spacecraft" is long.
"'Miracle': ESA reconnects with lost spacecraft" is opaque.
The first four words of the article are, "The European Space Agency..."