There are several ways to improve quality, not all upscale method do the same, some AI methods denoise the image again basically generating a new image, you can earn quality instead of losing.
However, usually they lead to even worse problems, such as disconnected details, too much sharpness, blurry, missing elements, wierd colors, seams etc.
This AI software shows good results but it will completely depend on the image, there is no definitive method or software that works everytime on any type of image.
No matter what you do, after having a required megapixel image, you should open the image, analize with 100%, 200%, 300% zoom and seach every corner for: crooked lines, malformed details, blurs, artifacts, light noise, chromatic noise and chromatic aberration.
You will need to improve your photo editing skills to solve those problems (I've never made an AI image that didn't need a treatment, there's always a little artefact or a wierdness) without make things worse.