I once heard that all our muscle are determined and working out only makes them look bigger but the limit is always the same. Is it true? Any of you went from nerd e-gamer physique to chad physique?

I look like this: https://www.tomic.com/wp-content/uploads/2019/10/how-to-gain-weight-as-a-skinny-guy-1024x683.jpg

Is it possible to get the physique of a 6+ foot chad person? Or the max I can do is a defined muscle but still small body? How do muscles work, looking for some information especially from the seasoned lifters here. (20 yo, 177 cm, fat ass and thighs, tiny upper body, fatty belly. 32 cm arms.)