https://en.wikipedia.org/wiki/Novo_Nordisk_Foundation
There are other similar examples like Ikea.
But those examples are for mature, established companies operating under a nonprofit. OpenAI is different. Not only does it have the for-profit subsidiary, but the for-profit needs to frequently fundraise. It's natural for fundraising to require renegotiations in the board structure, possibly contentious ones. So in retrospect it doesn't seem surprising that this process would become extra contentious with OpenAI's structure.