The Invincible

To gain this achievement you will need to take the Road to the Landing Zone path earlier in the story. Do not take the path to the alliance base.

For this achievement you will first need to follow the peacemaker dialogue below and also after completing this achievement you should be able to reload your save and do this part again to work on the Another Giant achievement.

Head to the condor at the end of the game and go to Rohytra.
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]'.
Then shortly after select 'In short? This is how evolution works'.
Now when Novik asks if you agree about them being invincible select 'I fully agree. We shouldn't attack'.
Rohytra will ask what else we can do if not attack, select 'Evacuate from here'

Rohytra will be done with one press of a button left, but he won't be able to do it and will stand down. You should now move into the hibernation chambers to get this achievement done.

Once you're in the hibernation chamber with Rohytra he will again ask you if you're still wondering if you should go to the nest, so this time select 'I decided to go' and some time later you will appear at the nest. Follow the nest to the very end and you will gain this achievement.

If you need more help with this you can follow my video guide below which will start at this achievement:

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.