A single playthrough of The Last of Us: Part 1 will not grant the player enough supplements or parts to fully upgrade Joel’s stats and weapons. Upon returning for a second playthrough in New Game+ Mode, the loot a player can gather will be regenerated, but stats and weapon upgrades will remain where they were from the first playthrough. By playing through the game a second or even third time, players can gather enough supplements and weapon parts to fully upgrade Joel and his weapons.

https://screenrant.com/last-of-us-remake-best-things-after-beating-game/