The current Paint.NET is really good and obviously has much more features compared to since the version from 2009. But it's not FOSS which can be a deal breaker for some.

If FOSS then Pinta [0] is the best option imo. GIMP is not bad either but feels very janky and all over the place sometimes (lacking some elementary features while overblown in other departments)

Krita [1] is the other one I'd recommend though it's a digital painting app, not a image editing one. But you can do edit images with it

0, https://www.pinta-project.com/

1, https://krita.org/en/