Nothing more dangerous than a bored billionaire.

I might mess with countries just to mess with them. Help countries I like.

I'd play the deep state game, with the goal of undermining deep states. I would install candidates that run counter to the establishment, no matter where the establishment stands, all to make the government as limp-dicked as possible.

First thing start using my new Vatican Interlibrary Loan card to check out all the hidden history and technology information I could to find out a better understanding of the truth.
Establish an R&D division working on occulted technology, Tesla, Schauberger (thanks whoever posted that one) technology.
Would need an OPS and Counter-OPs division, but those would be supporting the R&D and knowledge/development objectives above.
Might be able to open an occasional mind or so opportunistically along the way, and would make it a point to do so. Of course we already see the masses aren't much interested in that, so no need to bother them.
Wouldn't worry too much for having a particular legacy, other than that the R&D division goes on in a similar manner.

I'd give a billion to the shriners a billion to one or two other things quietly and keep laying pipe and farming.