If you want to donate to the Optimism Foundation's retroactive public good funding, you can send ETH, ERC-20 tokens, or NFTs to the ENS address retroPGF.eth. It is supported on Optimism as well as Ethereum mainnet.
Anything donated goes to the next RetroPFG round. RetroPGF is governed by the Citizens House. These funds do not go to OP Labs or the Optimism Foundation, with the exception of the foundation helping distribute the funds according to the Citizen Houses decisions.