In an all advancements speedrun, is the how did we get here achievement required for this category? Apparently it's secret so i have no idea.

Yes.

Usually it's something which in real life would be interesting, impossible or unbelievable, or an easter egg. But, since you mentioned 'How did we get here' I assume it could be something like getting to the place where llamas or parrots are. Something like in the April 1st snapshot... Or maybe to break the bedrock in Nether by one of those old methods, well, not sure if they work anymore ever since...

@Glacier_wuff14 Its to have every effect applied to you at the same time. Yes it is included.

this will be hard includes bad omen hero of the village levitation and literally every other effect in the game

@Lezzy OH! I so didn't expect it to be that difficult. Great luck with that... Don't you need to have 8 active beacons around you? Then every special arrow in a dropped above you right above the 9th beacon could work. I might be missing something...

Yes, it’s included as well as the other secret advancement arbalistic. Both of them require a setup that you have to train before running AAdv.