Nobody Wants to Die

To get the "good" ending, you need to side with the murderer when possible (that was the theme I was following in my second playthrough):

I made the following decisions (none bold probably optional):

• shoot the guy at the end of the Icarus investigation
• believe in an afterlife / choose death when talking to Sara after the Icarus investigation (foreshadows the ending)
• close the hidden passage after investigating the first crime scene again
• blame Green when talking to Sara at the museum
• do not shoot Salma and throw your gun away at the end

Edit: Possible that blaming Green is the only required choice to have the option of throwing your gun away later, which triggers the "good" ending. But I haven't done a third playthrough to verify.

In my experience (and I also searched a lot of forum & discord threads for it) this all comes down to two moments:

When you are in the Old Museum, Sara asks you if you think "The murderer is behind all of this" or if you think "Green is behind all of this". This happens after the third and final board-mini game.

Choose: "Green is behind all of this"

This makes your playthrough ready for one final moment, where you basically choose between a good and a bad ending.

You will get into a standoff with Salma if you choose "Green" in the museum and you can either shoot her or throw away your weapon.

Choose: [Throw away your weapon]

The dialogue before doesn't matter at all, I always chose something different and it played out the same.

So if you want the Anguish and the End of Deadly Dreams-achievement, make a backup save.