Social Login with: LinkedIn, Gmail, Apple, Facebook, Twitter, etc. (+email as option)

AND/OR

2-Step Email verification: Make the user go to the email provided inbox and click a verification button link OR get a temporary code to be inserted to validate the email as well.

I'm surprised that none of the above is not already implemented in such app since day 1, since this is your biggest problem that clients need you to fix. Not a page content builder......