Covers without an app or photoshop?

So, I have already made a topic with splashes and all that jazz but now I am making my cover. Like I said in the splash one, I would like to make one without having to get photoshop or get an app. I am doing this all on a Mac so if anybody could give me a link to a website or anything, that would be helpful!
(I do not want to use an art shop, sorry!) And I would not like to pay for anything!

Canva is amazing! Definitely recommend

Thank you so much! But, just in case, do you know any other websites where you do not sign up?

I like to use to color correct my pictures. The only problem (as with many editing websites have a pay wall with premium editing possibilites.

Is this free?