Ok so functioning labels are this weird idea that the autism spectrum is a line in which some people are at one end and some are at the other.
It’s assumed all those who are ‘high-functioning’ are verbal, good at communicating, not very sensitive, not too attached to routines, and can basically pass as allistic
whilst it’s assumed that those deemed ‘low functioning’ are the opposite
now in reality we are all a mix, for instance I’m mostly verbal but need to adhere to routines, I go into a monotone when tired and need fluffy animals to cope, I can sometims communicate effectively and sometiems make animal noises and flap
the reality is as some others have said its more like a buffet of different traits where we all have a very different mix and those ‘functions’ or traits fluctuate throughout our lives or even our days
and what functioning labels do to us varies on what you get labelled
those labelled ‘high functioning’ will be denied resources and assumed to be independent, they will be punished and chastised for struggling with anything and may be told they’re faking for attention when stimming or such
those labelled ‘low functioning’ are infantilised and assumed not too understand, they are given help even when it is refused and often are granted very little agency and bodily autonomy
so yeah, that’s a basic run down of what they are and why they’re wrong hope it helped!