If malware infects your computer, these files are the first thing attackers look for.
If you suspect your account has been hacked, you should immediately report it to Facebook using their dedicated "Compromised Account" page. This page will help you secure your account and regain control.
The search query "index of password txt facebook" is a classic example of Google Dorking
Regularly check where you are logged in and remove any devices you do not recognize.
Demystifying the "Index of Password Txt Facebook Better" Search: Risks, Myths, and Reality