Mmmm this works fine in MacOS (I did it years ago with the MS Paint binary).

Screenshot: https://rymc.io/mspaintosx.png

I think the non-web app that comes closest to MS Paint in functionality is GrafX2. Only other paint program I've seen that has selection-as-a-brush. http://pulkomandy.tk/projects/GrafX2

The interface is a bit different than MS Paint but it has these absolutely wild features, like colour cycling, where the colours can change while you're painting, which can be fairly psychedelic. GrafX2 is more of a clone of DeluxePaint for Amiga.

I'm no fan of mtPaint either.

The MS version at least can be wined without issue.

However, there are tons of lightweight image editors that run as fast as MS paint and offer more features; have you tried Pinta ? or gnome-paint ?

I disagree about usability. Probably most people just used MS Paint first. MS Paint has different tools and different brush-tip (widths) for pencil/brush/spray-can/eraser that all do essentially the same thing (okay, the eraser's right click mode is different, but hardly anyone knows about it), and then the line/curve/box tools all have _their_ own width. This is all unified into one global brush/pattern option in mtPaint that everything uses. The zoom levels are better too. I think the only thing that's not obvious in mtPaint is the eyedropper.

The one thing I like in MS Paint is the controls to resize the canvas near its edges. Most other programs make you go through a dialog or select and then trim to selection.