Sign into an existing account

I use my own domain and server. Any site that requires a website gets its own email address and then once I don't need it anymore I delete it. Problem solved.

I use https://10minutemail.com/ but it's just to sign up for things which require an email when they have no business asking for it. You can keep hitting "add another 10 min", but it will expire when you stop.

Here's another which I have not used yet: https://www.guerrillamail.com/

I've been using Yopmail for several years.

I also have my own domain and can/have created unique emails@mydomain, but that's pretty fucking rare.