To unlock the Friend of the Crew trophy in Metro Exodus, you will need to find the guitar and teddy bear during chapter 3, Volga.
You can see the location of both the Guitar and the teddy bear highlighted in the image below:Metro Exodus: Guitar Location:
Climb to the top of the large tower, killing any bandits you meet along the way. At the very top, head outside onto the platform and you'll find the guitar resting against a railing.Metro Exodus: Teddy Bear Location:
Climb to the top of the silos. You can unlock the Firebird trophy at the very same location if you craft some Molotov Cocktails from one of the safehouses on the map before climbing the silos.
Kill the demon and then directly below the nest you will see the teddy bear next to a red tricycle.
When both have been collected, you will unlock the Friend of the Crew trophy.