Here's how you can find it on your iPhone or iPad:
Open the Settings app
Tap on your name at the top
Tap on "iCloud"
Scroll down and tap on "Hide My Email" under iCloud+ Features
Scroll down and tap on Perplexity in the list
(If you don't have Perplexity in the list, it's likely you haven't used Apple Relay)Click and hold the email to copy the email
You can use it to sign in to your Perplexity account