Why does a subscribed mod not work? Is reloading a save enough?

After subscribing and finishing the Steam download, enable the mod in the game's mod list and restart the entire game. Returning to the menu or reloading a save is insufficient. Current loading requires subscription, an existing downloaded directory and an enabled whitelist entry. First-time runtime preparation also takes time. Check subscription, download, enablement and restart, then version compatibility and conflicts. Early statements that mods cannot add functionality are not reliable current limits.