I am not sure how it compares to recent versions of Paint.NET, but on my Apple desktop computer, I like to use Aseprite [0] (which is also not free). At the very least, Aseprite seems to have more features compared to the Paint.NET version that came with my Windows 10 installation (I think).
It's more of a graphic program for game design, but still very good in my opinion. And multiplatform, so usable on Windows and Linux as well.
Aseprite is free if you compile it yourself [0], and can still be used for commercial purposes if compiled this way [1]. But I recommend buying it anyway to support the project.
It's more of a graphic program for game design, but still very good in my opinion. And multiplatform, so usable on Windows and Linux as well.
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[0]: https://www.aseprite.org/