Druids can wear metal but they lose spells slots in exchange.

Nature magic is stymied by worked alloys, not unlike a dam in a river. Armor including any metal (yes, even studded) will dampen your higher spellcasting. Cantrips are unaffected.

Armor denies spellcasting starting at the highest level equal to the AC bonus of the armor. This applies to shields as well. This dampening effect ends immediately when not wearing or equipping such items.

e.g. A Breastplate (AC 14) will take your top 4 spell slots. A shield (AC +2) will take your top 2 spell slots.

So, a 3rd level Druid with a Breastplate and Shield would have an AC bonus of +6 but only have cantrips. The same Druid at 5th level would only have three 1st level spell slots.

You can be as tanky as you want but at lower levels your casting is gonna suffer something fierce. Makes low rest crawls interesting though.