And that's why European Union introduced the Digital Markets Act. By March 2024, Meta will need to give a way for third party clients to communicate with WhatsApp users in 1-to-1 chats. Group chats will probably follow 2 years after.

In addition to the other advice given in this thread, set an autoreply in your gmail that telld you that you have switched email addresses and include your new address. This way, people know of your new email address if someone still manages to mail you on your old email address.