How do I paint windows like stain glass?

Here are some ideas: https://www.hometalk.com/search/posts?filter=stain%20glass%20windows

I'm not very artistic so I would check into this company if I wanted to get that look. They have a huge selection of window films and most are removable if you want a change.

https://www.decorativefilm.com/product-list?utm_source=bing&utm_medium=cpc&utm_campaign=S%20%7C%20US%20%7C%20Window%20Films%20General%20%7C%20Alpha&utm_term=decorative%20window%20film&utm_content=decorative%20window%20film

These Hometalk Faux stained glass projects might be helpful.

https://www.hometalk.com/diy/windows-doors/windows/s-19-fantastic-techniques-for-faux-stained-glass-38444776?

https://www.hometalk.com/diy/paint/cabinets/combine-elmer-s-glue-and-acrylic-paint-for-this-one-of-a-kind-cabinet-42051118?

There are kits just for that. Michael's. Hobby Lobby. Probably Jo-ann. Probably Amazon.

On eBay you could buy the kit to do that it works great