According to Healthline.com,
Where gender dysphoria describes the feeling of discomfort or unease when one’s perceived gender doesn’t match their internal sense of gender, gender euphoria is when someone’s perceived gender aligns with their sense of self and causes them to be happy and feel at ease...
Gender euphoria can look and feel like many different things. It’s ultimately about being happy, confident, and comfortable. Often the feeling of happiness, peace, and the feeling of being “right” will align with your gender.
https://www.healthline.com/health/transgender/gender-euphoria#definition
Nowhere does the author mention dissociation or state that "gender euphoria" can only be achieved by ever-increasing efforts to change one's gender.
Considering that alleviating gender dysphoria can be literally life-saving for some trans people, I am more inclined to accept gender euphoria not as some sort of temporary high but as the feeling cispersons have of belonging in the physical body they inhabit; of being comfortable in their own skin.
In short, this transphobe is full of it.