Start a new game choosing location, loadout, faction, rank, money and more things from your election, reaching some kind of "free play" mode. Intro and tutorial will be skipped and main mission disabled.
This is intended to play a "new game" role-playing free play combined with overhaul mods like "Modular Hard Mode" or "Desolation", accompanied by A-Life mods like "Shay's Living Zone" or "A-Life Found A Way" and all the mods you want. As the game world is in the initial stage, you may encounter some closed doors/ways and some convenience tricks are used for being playable.
Depending on your faction relationship, you can play secondary (blue flag) missions, repeatable tasks/quests offered by some main NPCs and exploring The Zone and its many unrevealed secrets, mysteries and details. Main mission is disabled by default. Faction system in STALKER 2 is too underdone, don't have high expectations.
https://www.nexusmods.com/stalker2heartofchornobyl/mods/1211



