One-click unsubscribe (or RFC8058) is provided by some email clients that allow you to quickly unsubscribe from a sender.
Example from Proton Mail:
From Mac Mail.app:
All forwarded emails from SimpleLogin provide this one-click unsubscribe button that allows you to stop receiving these emails by clicking on it, which will disable the alias. SimpleLogin will also send you a confirmation email.
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 receives emails from other senders.