When i code a prototype, am i supposed to code it in a strong e.g. MVVM architecture or to code it however i know possible?

Since it's just a prototype, maybe just make it work. Instead of thinking about it's architecture and long term health of your code. That comes later when your prototype is accepted

I'd say that writing super shitty code is always a bad idea unless you are in a real hurry. However, if it's just a prototype, perhaps spending a reasonable amount of time on it is more important than making it perfect from the start.

@norman70688 You're right, but he said "strong e.g. MVVM architecture" so that can have a lot of code before making something work especially for just a prototype

Prototype == finished product
At least to management.