Welcome to the forum! I have been meaning to create a post to ask the same question. I have never owned a matte color car before and to be honest, I have never really taken care of the exteriror of my previous non matte paint cars. So I have little knowledge about how to best keep a car clean. haha
I really like the Frozen portimao blue and decided it was the color for me when I visited my local dealer and viewed their “color wall”. Because of how amazing the color is, this time around, I want to make sure the I keep the car clean and spectacular.
As for your question, so far youtube has given me some leads.
This video talks about how to wash a car with specific soap for matte paint.
This one talks about a product to help “protect” the paint.
I am no expert here so I can’t vouch for the products used in the videos.
The last thing I have read about to help protect your paint is a paint protection film. There are so many out there that I do not know which would work best for matte paint. You also you run the risk of the film giving your matte paint a glossy look.
Hope some of this helps. I too am very interested in hearing other suggestions.