This is referring to physical improvement of a person's body - in terms of development of facial features or muscular improvement - in order to make oneself more attractive or easier to like.
This term is derived from a video game type idea of statistics (stats) and a levelling system where looks is one of those stats and max means the stat has been filled to the limit the game set.
"I spent the weekend looksmaxxing, I'm about to pull some," said the cringy 12 year old.
"Looksmax yourself dog. Man, you ugly as hell tbh" the 17 year old said to his brother before his first date.
The act of altering one's appearance in order to become more attractive. Can be 'soft' (meaning more normalized, less-invasive, and non-permanent methods of improvement, such as getting a haircut, going on a diet, or wearing makeup) or 'hard' (more intense methods such as plastic and cosmetic surgery and steroids). The term is popular amongst incels and femcels but the majority of people on the planet participate in looksmaxxing in some way or another.
"I am a deeply unhappy person. I think I am going to fixate on looksmaxxing to become more attractive instead of addressing the core issues that plague me."