https://getpaint.net/
Some other random company got the url "paint.net", so confusingly you need https://getpaint.net/ to download the product paint.net
For those unfamiliar, it's a free art program that's... idk 80% of what photoshop is? But you can install community-made plugins to add features (shoutout to Grim Color Reaper).
Also on their download page, you want this one:
If you do the microsoft link, you'll have to pay microsoft. For a free product. That microsoft doesn't own. Dafuq.
The paid version from the microsoft store helps to support the product; however I suspect the devs will get more bang-per-buck if you DL the free version and make a direct donation at https://getpaint.net/donate.html