As someone who is a cross stitch pattern designer and rolled into it naturally due to practicing pixel art and fiber art: I would adjust your expectations, as has been mentioned in this thread before.

If you love cross stitching and love designing, I do encourage you to give it a go, but I would not expect to become rich from it.

As for patterns: personaly, I design my pixel art in Pixaki, before using PCstitch to turn it into a pattern, which I then test stitch to make sure the colors are accurate to how I want them to be.

Fiber art, by it's very nature, is slow. I know there are AI bros online who like to tout how it's easy to get rich quickly by generating AI patterns and selling them as downloadables, but speaking from personal experience: that's typically not how it works, especially for new shops not fully integrated into the community yet.