The Invincible

1. At the bridge go through all the dialogue with Rohytra selecting whichever you want, ideally being against the bombs until you come to the Necroevolution theory. DO NOT choose 'There's no point speculating' instead select 'Necroevolution theory [discussion]'.
2. Then shortly after select 'In short? This is how evolution works'.
3. Now when Novik asks if you agree about them being invincible select 'I fully agree. We shouldn't attack'.
4. Rohytra will ask what else we can do if not attack, select 'Evacuate from here'

My video guide below will begin at this achievement if you need more help:

In this rather long video I will show you how to get all achievements / trophies related to endings.
It's all in one video as you have to replay the ending sequence in a different way each time.
The first critical choice however is when you are about to go to the Landing Zone to evacuate. In short - don't. Before you do anything backup your save file and go to Alliance Base. If you already did go there don't worry, you can still get a lot of those achievements and you'll get the rest after replaying from that point.

I also recommend you do a backup of save files once you reach the bridge of the Condor or after finishing the game for the first time. Just in case you want to return to that point later.