2021 rdx with 35k to me seems like either gear oil leak between transfer case and transmission took it to the dealer and tech said is grease leak and shouldn’t be concern

 

Several people here have noticed this. I cleaned mine off several times, and it always comes back. Mine has always been much less than in your photo, but I have cleaned it 3-4 times in 32k miles -- so maybe about the same.

 

Acura is full of crap. They dismiss all signs of leaks while car is under warranty. I have slow transmission oil sip that makes transmission case slightly wet. All dismissed, the excuse that in order to be covered by warranty it actually has to drip down to a cover plate. Acura warranty coverage has become the worst, back in the day this would have been covered with no questions asked.

 

I noticed the same on my RDX and started looking around the engine for leaks. Found out the valve cover gasket is leaking badly especially on the back right side of the engine with only 44k miles. It is possible that oil is dripping down to this area in the picture. I am having the gasket replaced and will monitor the leak around the transmission area.

 

I would take some pics, spray it with brake clean and check again in a week, take more pics and just provide that to your dealer if it comes back.

Use the pics to enforce that something is indeed not right and they need to investigate since it's under warranty.