I switched from Chrome to Firefox in 2019 because that's when Google adopted Manifest V3 and I never looked back. There were already articles then describing how it'd break ad blockers, and Firefox had at the time just recently released their "Quantum" overhaul which drastically improved responsiveness.
I'm a bit surprised it took five years for Google to drop support for Manifest V2, but the threat has long been there.
It was released. The Azure Flute and the event where you meet and battle Arceus in the Hall of Origin in DPPt was indeed never released, but this is different.
Arceus had various distributions in 2009-2010; the US one was at Toys R Us for example. Trading that legit Arceus to HGSS and then bringing it to the Ruins of Alph triggers this event which takes you to a special location where you can choose one egg of either Dialga, Palkia, or Giratina.