I keep seeing people saying this about Politico and it's total FUD. I have friends who work there and it's pretty firewalled from Axel Springer. This conspiracy theory about the Politico portion seems to have started in r/Europe and r/WorldNews a couple months ago and kept getting repeated since.
Matthias Doepfner’s mails and chats including pressure to upsell the FDP in Springer’s papers leaked in April and were widely reported. That’s not a conspiracy theory. If it were, Doepfner could sue. He didn’t.
So Döpfner (who is on record ordering his "journalists" to push the FDP in the last election) just bought Politico and doesn't make sure they follow the directions he sets for all the other publications owned by Springer? Seems unlikely.
A firewall operates purely in the physical world and relies on immutable properties of the physical world to function. To use it as a metaphor in the intellectual/political world (where nothing is immutable) is exceedingly unhelpful and I would say, often deliberately misleading. There is no 'firewall' inside Axel Springer, there is no 'firewalling'. Talk like that is pure nonsense.
Politico is DC slang for someone who works politics adjacent (hence why their competitor "The Hill" is named that)
Politico started as a blog and newsletter on the Hill back in the late 2000s/early 2010s where we'd leak gossip, but they had amazing product-market fit and ended up opening an EU office a couple years ago (lots of Hill adjacent people also worked in Parliament and Bundestag via early career Atlanticist programs).
A couple of my own quotes have ended up in Politico