We have a lot of experience with streaming and want to start all over with Twitch, so we're looking for a designer to do the designs for banners etc. For us.
Take a look at Fiverr
Either ask an edger who is familiar with graphics,
or ask in a Twitch forum there are often people who do that for little money
or ask in a graphics forum such as Designcommunity.club or tgraphics.de
there's something free for newbies and non-commercial users
(Condition is, however, a precise description of your wishes with examples that you like)
Or hire a graphic artist, e.g. At fiverr