No one actually knows for sure what drops are affected with this buff, because in the original blue post about Collector’s bounty, it said:
All pre-Dragonflight legacy mounts from legacy dungeons and raids.
But then the youtube short that came out said,
All pre-Dragonflight mounts.
So which is it?
Are mounts from legacy world bossed like Rukhmar included?
Are world drops like mounts from BfA invasions included?
If someone could type up an official list (not Wowhead, as they are also speculating given that we have so little information) that would be very, very appreciated.
I genuinely do not understand why direct, fact-based communication like this is so hard to get. It is not unreasonable to want to know how a month-long event works.
World bosses are not considered raids, they are world bosses that are downed with a raid party, but they themselves are not considered raid content, hence the name World Boss.
Blue Post is pretty explicit that it is dungeon and raid mounts:
If you’ve been on the hunt for rewards that have been eluding you, now’s the time to get them. The following will have drop rates increased by up to 10 times (and in one case, 25 times!), while your chance for Transmog loot drops is doubled in legacy (pre-Dragonflight) raids and dungeons:
All pre-Dragonflight legacy mounts from legacy dungeons and raids
Eye of Sulfuras (Molten Core)
Golden Hearthstone Card (The Nighthold)
Bindings of the Windseeker (Molten Core)
Warglaives of Azzinoth (Black Temple)
Thori’dal, The Stars’ Fury (Sunwell Plateau)
I would guess that world bosses were left out because they were all pretty easily purchasable last summer during MoP Remix except Rukhmar.