Here is a piece of code that since today (27/09/2024) is FOSS:
function appendFOSS(text) {
return text + ", and this is FOSS";
}
Licensed under MIT since 2024 by Victor Bjelkholm
This is all you need in order to create Free and Open Source Software. Nothing more, nothing less. You only need the code to be public, and have a FOSS-compatible license.