They work by giving you a random email address that is available for a short time (ex. 10min) and an inbox for any messages you recieve during that time (ex. an email verification message from a Lemmy server)
I didn’t want to recommend a specific one, however Googling “temporary email” should give you several options to choose from.
Are there really people out there not using a password manager in current year?
When I first set up my password DB I forgot my master password. Fortunately that didn’t happen on my second. I still have the locked first db.
Many people don’t like putting their eggs in one basket. Which I get. But imo as long as you’re properly securing everything as well as you can, most decent passwords managers are trustworthy enough.