Google will no longer support the use of third-party apps or devices which ask you to sign in to your Google Account using only your username and password.

¿may anyone recommend a free mail service that doesn't require a phone number or another mail account and doesn't use only OAuth works with mutt?

I don't know what mutt is, but I have a spare account using:

Tutanota

mutt is a mail client (console)
it may use the IMAP or POP3 protocol to retrieve the mail and sadly tutanota does not support either

what about your ISP? Most provide N (usually 4 or so?) boxes free along with the service, and most of those support both pop3 & imap.
yahoo mail can be pulled this way, or could last time I checked.

https://protonmail.com/ apparently allows protocols.
https://protonmail.com/support/knowledge-base/imap-smtp-and-pop3-setup/

It's pretty privacy oriented, but I can't remember if it needs a phone number during signup.

https://posteo.de/en 👍

Mail.com ?

It is pretty simple but useful service for e-mails.