One-click unsubscribe (or RFC8058) is provided by some email clients that allows you to quickly unsubscribe from a sender.
Example from ProtonMail:
From Mac Mail.app:
All forwarded email from SimpleLogin provides this one-click unsubscribe button that allows you to stop receiving these emails by disabling the alias: clicking on the button will disable the alias. SimpleLogin will also send you a confirmation.
You can also choose to block the sender instead of disabling the alias by using the One-click unsubscribe setting: this way only the sender is blocked but the alias is still active and receive emails from other senders.