No need to be "logged in" to a storefront to play a game you own.
Zachareee/goldberg_emu: A fork of Goldberg's steam ... - GitHub
Ensures that if a storefront ever goes dark, your library remains playable. Simplicity: Often just a matter of swapping a single file. Why "Unyielding"?
It famously allows for LAN multiplayer in games that would otherwise require an active internet connection to Steam servers. Setting It Up: A Quick Look
Where you can customize your "username" and other account-simulating features.