IMO thta deck is all wrong and should be rebuilt to be a multi level deck with all that seating replaced with a nice railing ideally in a metal. Is there a door under the deck ? I just think you are going to all the work of repainting the deck is just not nice .

This article has some nice ideas.
https://homedecorbliss.com/what-color-should-i-paint-my-deck/

I personally like it when a painted deck matches the house color. It looks seamless and more expansive, IMO

Whatever you decide to do with the deck (I agree with Patricia, you should rebuild it if it's been there for a long time), I think any brown color will look good with blue. As with any painting project, sampling is very important. I guess gray would work too, but I think brown is a more natural color for a deck.

Transitional Deck · More Info