Many replies seem to imply open source by default. Of course projects may have specific requirements, and open source is indeed a specific use case, but the majority of software is commercial, closed source.

Regarding compiler versions, many projects I worked on actually check that during the build because the code may only have been designed for or tested against a specific compiler/compiler version. In general upgrading the version of the compiler is an activity in itself because, indeed, this may require solving new warnings/compilation issues and a full test campaign.

That may be true for 'end user applications', but definitely not for libraries (thankfully). I use exactly zero closed source (precompiled) dependencies in my hobby and professional work because they are such pain to work with. Thankfully these days there's an open source alternative for pretty much everything, 15 years ago the situation was much more dire.

But when I look at the tools and applications I use daily, there's only two important applications that are closed source: VSCode and Chrome (and even this is debatable because both of those tools are just thin wrappers around Chromium: https://chromium.googlesource.com/chromium/src.git).