Facebook have released a bunch of good-quality open-source libraries and tools. Not just zstd, rocksdb, folly, flow, hhvm and other niche things, but also PyTorch and React, staples of two industries.
Since they are honestly open source, they have been inspected a lot, and, if they included any data siphoning, that would be long known, and long since deleted.
Their technical achievements are not my domain. But I know behavior patterns, since Facebook's platform was built to harm peoples ability to choose for themselves, I consider it a blight on humanity. I doubt they have any interest in serving the common good. But I hear that you don't share my skepticism, time will tell.
Since they are honestly open source, they have been inspected a lot, and, if they included any data siphoning, that would be long known, and long since deleted.
I don't share your skepticism.