That's simply not true. Musk is not a open source or public domain advocate. He is a profit-driven entrepreneur.

His current ambitions to create a OpenAI alternative is not for open source or public domain, it's to counter the leftist agenda (coincidentally also racist and sexist) that OpenAI has been pushing with their latest products, as he has multiple times in the past proclaimed he is politically neutral, antipolitical/anti-establishment and expressed views that could be understood as conservative.

Obviously, he counts on it being profitable, as OpenAI has demonstrated. The question only is - how does he do this without entering a conflict of interest with Tesla, which is mostly an AI company itself?

It's not much different from the reason he provided for buying Twitter (other than being forced to), which is countering Twitters control of the narrative into one that stifles conservative views and promotes liberal ones.