Where to catch Lugia?

While tackling Victory Road, I came across the idea of catching Lugia after defeating the elite 4, however I remembered in the Audrey questline, Lugia was present. Double-checking the wiki, they were on Audrey’s team, and the wiki doesn’t say how to catch it. How do you catch Lugia if possible? It’s one of my favourite legendaries in my least favourite region (Johto)

You need to first beat the elite four and then also complete a post game mission where you save audrey, and after you do that quest, lugia will appear in the area where you first battled audrey, on top of a waterfall. (And yes you also need waterfall from the holon region)

Check this wiki Page’s Pokémon section for more information