For the most part I think the aim is different at it's core. Beauty standards are a bit whimsical and enforced from without. You are rewarded by society for conforming to these standards which feeds back into the desire. It's similar but Gender Euphoria and Dysphoria come from within. Some of the things it acts on aren't beauty standards and the rewards from without are often a mixed bag of good and bad because society doesn't reward your specific goals.
The reward is feeling like yourself. Feeling seen and not having people comment on your appearance with gendered pronouns that make you feel weird or bad. If you are ugly society usually doesn't comment on it directly to your face because that is seen as harmful or rude. But being trans people comment about your body every bloody day without knowing it : when they call you he/she/ma'am/sir. Each time is a reminder of the part of your physical experience of life reflecting you in a mirror of words that are never value neutral to you only to the person speaking unless otherwise told.
Would body positivity be possible at all if the commentary on everyone's most vulnerable physical features were offered half so often as they are for us?