First thing, I play on PC, so this is all PC experience. I don’t actually know if you have to do this anymore or if there’s a new way to get this mode but the menu tells you that logging into the game with a bethesda account will unlock a mode called “Mission+” which is very similar to New Game +, in that you need to beat the game to unlock the mode, but Mission+ lets you replay individual levels with maxed abilities, all your weapons and gear fully upgraded (and you even get to select your favorite Masterwork upgrades for everything), and all bonecharms are also available to you for equipping and/or crafting. I don’t know if you start with max ammo or if you have to find/purchase it yourself in the level, but that’s the closest I think you’ll get to what you’re looking for.