BtbN/FFmpeg-Builds ? reverse-engineered prompt

Build me a simple way to produce static FFmpeg builds for Windows and Linux, with the same kind of setup this project uses. I want to be able to choose a target like Windows 64 bit, Windows 32 bit, Linux 64 bit, or Linux arm64, then pick a build flavor like GPL, LGPL, or nonfree, and optionally build from a specific release branch instead of master. It should bundle the usual dependencies, let me make either normal static binaries or shared builds, and give me a zip file in an artifacts folder when it finishes.

Please make the scripts easy to run with bash and Docker, and keep the build process reproducible. If there are missing pieces or current best practices I should follow, look up the latest docs online and adjust the scripts so they still work well today.