So far as I'm aware, the person behind https://pineapplefund.org/ is still unknown. Perhaps that's a good place to start.

If you're using fiat (USD, EUR, RMB, etc.) I would assume the only anonymous method is cash, or an instrument purchased with cash (money order, prepaid gift card, etc), mailed from a public mailbox with no return address, but of course that raises its own problems of ensuring delivery.

For fiat, I doubt any electronic method offers any real protection against subpoena, etc.