That was a couple years back.
I believe I compiled Love binaries on RetroPie (which didn’t have a Love package at the time) following the normal build instructions, except I configured a love.AppDir as install directory. Then I compiled linuxdeploy and linuxdeploy-plugin-appimage for ARM, and used those to finish the AppImage.
But nowadays that should be a last resort. Instead I would try compiling and installing Love on the Pi or other ARM device as normal, then following this: https://love2d.org/wiki/Game_Distribution#AppImages