This is another great way to get some cash while publishing Low content books /no content books. you can design some easy covers (paperbacks) and sell them on Amazon KDP. I'm doing that myself & it's earning me some passive income. 

For the cover design you can use :

• Adobe illustrator
• Adobe Photoshop 
• Adobe Indesign
• Canva ( online platform)
• ...etc

For the Interior design:

• Interior generator  (online platform)
• Powerpoint 
• Foxit Phantom PDF(Pdf editor)
• Canva 
• ...etc

I usually combine multiple platforms to come up at the end with much more satisfying design, Then upload it