Opensource

I have. It just goes nowhere. The number of people you need to sign off what is essentially a donation is just too high. You always hit someone who says "why do we need to do this?" and the answer is "we don't".

You need some actual benefit before most companies will actually pay money. It doesn't have to be huge though. Sometimes support is enough (as long as you don't also offer free support e.g. via GitHub issues). Phabricator did that and it seemed to work.

Open core also definitely works. My company pays for GitHub premium because we need the features - primarily merge trains.

They're very rarely going to donate out of the goodness of their hearts, and if you expect them to do that because you think they are morally obliged to then you're going to be disappointed.