blogs.windows[.]com/windows-insider/2023/09/07/background-removal-in-paint-begins-rolling-out-to-windows-insiders/
blogs.windows[.]com/windows-insider/2023/09/18/paint-app-update-adding-support-for-layers-and-transparency-begins-rolling-out-to-windows-insiders/
Paint isn't going to replace 3rd party image / photo editing software any time soon, but it is becoming more useful, and hopefully the more AI Microsoft adds, the more pressure will be felt by the companies making those 3rd party photo editors. AI is expensive, and it's also a gimmick, seen as an excuse to charge more than what we might feel reasonable. [In the article below, David Gewirtz talks a little bit about how companies are starting to charge more to pay for AI.]
zdnet[.]com/article/ai-is-a-lot-like-streaming-the-add-ons-add-up-fast/
In what I hope is a first [baby] step adding [actually useful] AI to Paint, Microsoft added simple background removal, and so that you can use it in a meaningful way, they also added layers and transparency. The basic idea is you open the photo with your main subject(s), import another photo with a new background on a new layer, move that layer underneath your main photo, and then remove the background on your main photo. Since the parts of the photo with the original background are now transparent, the new background shows through.
Right now, Microsoft is expanding both the ways you can use their AI image generation, and the quality of the images it produces, e.g., with Open AI's next version image generator. Hopefully some of that will also trickle into Paint, though for now, Paint's background removal is more of a cross between a demo and a new toy to play with... it automatically chooses the subjects or objects that are the focus of your photo, selects their borders or edges, and then removes everything outside those borders. Depending on the photos you feed it, both steps have [sometimes lots of] room for improvement.
Since Paint doesn't offer much in the way of tools to select the parts of the photo you want to keep, and because its automatic selection can be far from perfect, you might want to try tracing around all or parts of the stuff you want to keep using the eraser tool. That might help in some situations. Bear in mind that to make a convincing composite that looks like it's an original rather than edited photo, resolution, amount of noise, colors, lighting, shadows etc. all have to match -- the best you can do in Paint is to really carefully select your photos, e.g., having the light come from the same direction and so on.