Rare VS HeroicBashLauncher

Note there is an open source alternative to the epic launcher in case you don't trust it : Legendary (command line based) https://github.com/derrod/legendary Rare (standalone user friendly frontend for Legendary) https://github.com/Dummerle/Rare Heroic (another user friendly standalone frontend for legendary) https://github.com/Heroic-Games-Launcher/HeroicGamesLauncher

Can you utilize addtosteam.sh with this similar to how heroic did?

I've previously used Heroic Bash Launcher for that. It generates a script that opens the game in exactly the same way Heroic does, and you can then add the script as a non steam game.

The EUREKA moment came from a thread for CIV IV on a random Heroic Launcher Github thread. https://github.com/redromnon/HeroicBashLauncher/issues/38

Works for me with Lutris shortcuts and some native Linux games I have installed. Herioc shortcuts needs an extra step using Heroic Bash Launcher

You're probably better launching through heroic and not directly using proton. This project looks like it might add all your heroic games to steam automatically: https://github.com/redromnon/HeroicBashLauncher

Heroic Bash Launcher

Use Heroic Launcher (find in desktop mode via discover (flatpack)). Install Windows versions to take advantage of Steam/Proton. Sync saves using Heroic Launcher too (be careful the feature is currently in Beta, but working fine for me in D:OS). Install the shortcut in your steam library using Heroic Bash Launcher, job done.

For heroic installed games, i used https://github.com/redromnon/HeroicBashLauncher to add steam shortcuts for individual games.

But for Heroic, afaik you need this, though I am still working on the guide and can't 100% confirm.