Once a hacker finds a working combination (a "hit"), they may steal funds from PayPal accounts or resell access to premium streaming subscriptions on the dark web.
Sharing, selling, or using these lists for unauthorized access is illegal under various data protection and computer crime laws. How to Protect Yourself
Never reuse the same password across multiple sites. If one site is breached, a unique password prevents attackers from using that "combo" to access your other accounts.
Even if an attacker has your password from a combolist, MFA can prevent them from logging in without your secondary verification code.
If you are concerned your information may be in such a list: