This is true for ALL websites, not just Portfolio.
Mailto links don't DO anything unless users have an email client like Outlook or Apple Mail set-up on their devices. Most people don't use email clients anymore, not since web-based email systems like Gmail, Hotmail, Yahoo, etc... have replaced them. An actual contact form is the most reliable way for your site visitors to reach you. It also helps reduce spam.
Portfolio makes it simple with the one-click Contact Form Module. See link below.
https://help.myportfolio.com/hc/en-us/articles/360036484493-Contact-Form-module
Post back if you have any questions.