See screenshots 4 and 5 here:

I wondered what would happen if I changed "m68k-apple-macos-gcc" to "m68k-amigaos-gcc" in my Makefile?

Added just enough code to get it properly building, then sketched out a bare minimum video driver, using CyberGfx to handle 32 bit pixels.

Will upload to my github soon.

git clone https://github.com/laulandn/sdl2macos9.git
(Yes, same tree for MacOS 7/8/9 also)
cd sdl2macos9/SDL-main
(Don't use configure, uses gcc from AmigaPorts or elsewhere)
make -fMakefile.amigaos3
cd test; make -fMakefile.amigaos3
Try out testcopyrenderex, testsprite2, teststreaming etc on Amiga or in emu.

Certainly won't win any speed races, but it's a start.

Very early (and limited) AmigaOS 3 versions of SDL2_image, SDL2_mixer, SDL2_ttf, and SDL2_gfx now building. They work as far as they can.
At https://macintoshgarden.org/apps/sdl2-macos-9-rough-draft