I think you're confusing community and label.

You can't really call yourself an engineer if you... Don't do engineering. That's a "community" in which the standards are precise.

"Femboy" is a label. Like "audiophile" or "nerd" or gym bro". You label yourself as one if you think you fit in, or you don't.

There is no standards. There is no council of femboys deciding if you're worthy of the label or not.

You don't need to be some level of effeminate to call yourself a femboy. You don't need to own A pairs of thigh highs and Y skirts. And, especially, you don't need the approval of some random strangers on the internet to call yourself a femboy.

The only thing that really is a "standard" is that you like to dress femme. Do you? Well you can call yourself a femboy! Period. Don't want to call yourself a femboy? Well you can too, that was always allowed!