While changing oil i noticed this leak down the side of the transmission. It looks and feels like anti seize. Has anyone else noticed this on a 2021 RDX?

 

doesn't look like a leak...it does however look exactly what you described it as...
looks like some sort of sealer, and when squished together it over flowed.

I would clean it. and check it after a few thousand miles to see if it is indeed a leak or perhaps was left over/a spill.