gmail works very well - if you're willing to let them read your email.
Apple device owners can use their icloud accounts, which also works well. Its part of the price of an
Apple product, so its ad
free. Apple users can also use the new Sign In with Apple that generates anonymous email addresses ... but with both of those you are captive to keeping an Apple device so not for everyone....
ProtonMail does have a free option, as well as paid ones with higher levels of service/features.