The only term I could think of is defeminization.
It seems like most people understand what emasculation is and the things that cause it.
What are some examples of situations that can cause the feeling?
Edit: changed effeminization to defeminization.
I’ve looked into this before and there is no word or equivalent phrase for what you’re talking about.
Effeminization is more about men seen as too feminine so it’s not it.
Inadequacy as a woman/girl is I guess the closest. There are idealized forms you’re pushed to be like when you’re growing up and into adulthood. Breasts are probably the closest stand-in for testicles in this context but it’s not a perfect one.