Metro Exodus story changes a bit depending on the actions you take in the game. This also applies to three characters in the game namely Duke, Damir, and Alyosha which are found in the Volga, Caspian and Taiga levels respectively.
How To Keep Duke Alive: You can keep Duke alive by completing the bridge sequence in complete stealth.
How To Ensure That Damir Stays Back In Caspian: You need to get the Family photograph from the area beneath the Lighthouse. We have a complete guide for that. You can check that out here. Furthermore, you should not raise an alarm in the final mission.
How To Ensure That Alyosha Doesn’t Get Wounded: Do not attack or kill the Pioneers in Taiga. You should just use stealth to ignore them completely.
So, as you can see, the key gameplay mechanic is using stealth as much as you can. If you get it right you will unlock the ‘Full Strength’ Achievement / Trophy in Metro Exodus.
For more on Metro Exodus, check out our following guides!