Transmaxxing is a term from incel culture and it refers to the way som male-identifying incels decide to transition and live as women, as they think living is a woman is easier than living as a man. They also think that this will improve their love life and give them access to sex.
The underlying incel world view is that the incels are failed men who cannot live up to the masculine ideals of society and who therefore never will be happy or accepted as who they are. Nor will they be able to attract women. The term incel means "involuntary celibate".
Members of the incel community are often love-shy and introverted male assigned people who have a personality or a life experience that make them feel excluded from dating and courtship. This makes them extremely lonely and it is probably the despair that follows from the idea of never being able to have a good relationship with a woman that brings them to the incel community. In the incel community their deepest fears are confirmed, and they take comfort in the fact that they are not alone.