But can you resize without antialiasing, and does pasting trigger antialiasing?

There's this https://www.windowsphoneinfo.com/threads/why-does-resizing-m... (made confusing by the next person talking about Paint 3D, a different application) and this https://learn.microsoft.com/en-us/answers/questions/3991946/... (made confusing by the person being an artist and talking in peanut butter metaphors).

I can't reproduce any of those issues. When drawing the indicator snaps to a pixel, so it's perfectly clear where it's going. When I draw a line, it's pixel-perfect when moving the control points, likewise after it finalises. And when I copy a section of the image and paste it back in, it's pixel-perfect as I move and when I finalise. There doesn't seem to be a true resize; all I seem to be able to do is change the size of the canvas, which doesn't add any kind of aliasing.

But I've only used the program for less than 5 minutes, so maybe it's configured differently?

Yes, resizing within Paint preserves pixel-level color. I just resized a single pixel dot to about 14x25 without aliasing.

I don't know why you are so concerned, but it's incredibly easy to test these questions if you really want to know.

And create single-pixel images. My most used application of Paint by far is creating single-pixel PNG files to work around the fact that "solid color" is not an option for lock/login screen backgrounds.