A PayPal.Me/username link proves the person has an active account. They can share this without exposing their email.
(if you're a developer looking to build your own) paypal valid email checker
While there are legitimate uses, "PayPal Valid Email Checkers" are frequently associated with cybercrime. They are a staple tool in the arsenal of fraudsters engaged in "credential stuffing" or "account cracking." A PayPal