It’s like Google used to do with Gmail, only moreso. Like squared.
I still have a Yahoo account, but have transitioned over the past few months to ProtonMail from my Gmail account and my Yahoo account.
I highly recommend Protonmail. They do have a free version, but the paid version isn’t that expensive. I also use ProtonVPN for a bit more privacy…..
Remember, if the service is free, then you are the product….