Ok, $100m question. How to remove toxic approve flow to send some ERC20 tokens? Can I just attach a finite amount of ERC20 tokens to a transaction the same way I'm doing with ETH?

ERC20 no, but ERC777 yes https://eips.ethereum.org/EIPS/eip-777

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btww you can send a ERC20 in a single transaction, the issue you're pointing is when this transaction need to do something else. ex: swap USDC for ETH you need to send the USDC and initiate the swap those two can't be done in a single transaction.

because there's 2 smart contracts involved, the token contract and the interaction contract, the token contract need you to author the transaction. by approving the interaction contract to use your ERC20 you're allowing him to author the transfer so after that you just have a single contract call.