Same with me. It seems to be a common problem with older plugin UIs combined with high-res monitors. I'm a n00b to paint.net so I'm not sure if there's a fix. Haven't found one based on my searches.
Hi, Just installed the pack on the Windows Store version and I seem to be having scaling issues on my 4k monitor for the Tools. As you can see in the attached screenshot, the lefthand menu buttons are tiny, the top menu items are cut off, as is the "OK" button on the bottom right. Any help would be appreciated.