Archetypes
This is what you need for a second archetype
You must purchase a second archetype item in ward 13 or come across one during game play (in this case, you bring the item to Wallace and, among other things, need a simulacrum to activate this archetype).
So possessing a second arcetype is not enough. This item must first be prepared for use, and that also costs materials.
When the item is ready for use, you can recognize it by a flashing exclamation mark on the archetype tab of your menu. Later in the game you will encounter or purchase multiple archetypes, but you can only actively use two at a time, and only the active ones are leveled.
So for a second archetype you need:
Save 1500 scrap and purchase a second archetype or pick one up during game play.
Give the item to Wallace in ward13 and pay him 5 lumenite crystals to prepare the item for use.
Activate the second archetype in the menu