Pretty I believe just means above average in appearance but not in a striking more universal way which would describe beautiful, a word more generally applied to females than males, or to describe an object or animal ( e.g. a butterfly, sunset, flower). It can also be an understated way of describing beauty whether physical or non-physical.
Handsome is the male equivalent of beautiful and more commonly relevant to males than females but can also pertain to more business-like objects and concepts (a handsome salary, a handsome briefcase 💼, a handsome pair of dress shoes) or a female who is good-looking but in a more masculine/authoritative way.
Beautiful can also describe a male who embodies and radiates both inner and outer beauty, not necessarily in a feminine way but in a way that can appear multi-dimensional to the observer. It can also refer to children, babies, puppies in a similarly generalized, unisex manner.
Pretty however can also apply to attractive males with more girlish delicate facial structures.
It also can just depend on one's perception.