This campaign won't use any rules concerning: "Resistant or Immune to Attacks from Non-Magical Weapons"
It's just not a thing in this setting, and monsters that have these rulings will be modified.

I think the game becomes more engaging when new resistances, weaknesses, and vulnerabilities are introduced.
Forcing players to carry a magical weapon just to remain effective feels arbitrary, and the same applies to special cases like silvered weapons.
This allows for more creatures to be designed with distinct weaknesses, resistances, and immunities.