It's not strictly required by the definition of open source, but....
A) If you don't provide builds and successful building is more involved then ./configure && make && make install, then you're pretty user-unfriendly.
B) If you aren't providing builds for target platforms then you probably aren't building for target platforms, which means part of your software has zero test coverage. Again, not a requirement, but it's fair for people to count that as a negative.
I used to distribute open source bindings to a commercial+proprietary library. I couldn't provide builds because I didn't have a distribution right to the proprietary license, even though I could test it on my own copy.
These days I'm having a tough time providing a build for macOS because my Python extension uses OpenMP, and there are several different ways to get OpenMP for that OS. See https://pypackaging-native.github.io/key-issues/native-depen... for details, including how PyTorch vendors Intel's libiomp while Scikit-learn vendors clang's libomp or GNU's libgomp.
Rather than deal with that mess, I provide source, and test with libgomp.