https://proton.me/support/addresses-and-aliases

If you joined Proton before June 2022, you could get a free @proton.me address (alicejones@proton.me) for a limited time in addition to the original @protonmail.com (or @protonmail.ch) address you signed up with.

This option is no longer available, but you can get a @proton.me address by upgrading to Proton Plus.