@Lolonois I've tried to see where is the problem on an multi-arch installation and check whether this is a packaging issue for the SDL2 packages we create. From what I can see, the packaging is ok, the thing is you need to have both packages at the exact same version and built using the same source.
I've build - on a clean env - 2 arch packages from RetroPie's SDL2 sources and they can be co-installed on the same system:
mitu@host:~/src/sdl.mine[cross]$ dpkg --print-architecture amd64 mitu@host:~/src/sdl.mine[cross]$ uname -r 6.10.11-amd64 mitu@host:~/src/sdl.mine[cross]$ uname -m x86_64 mitu@host:~/src/sdl.mine[cross]$ dpkg --print-architecture amd64 mitu@host:~/src/sdl.mine[cross]$ dpkg --print-foreign-architectures i386 mitu@rockman:~/src/sdl.mine[cross]$ dpkg -l | grep libsdl2-2.0-0 ii libsdl2-2.0-0:amd64 2.30.8+rpi6 amd64 Simple DirectMedia Layer ii libsdl2-2.0-0:i386 2.30.8+rpi6 i386 Simple DirectMedia LayerIt was easier to set-up a cross-build env on a PC, but I don't think things are different for the arm64/armhf combo.