Cannot login to backend/admin area

Disable all plugins by renaming plugins folder example plugins-deactivated via FTP and try logging in again. If it works means you can login to admin area (or not works) rename the plugins folder to its original name.

See this tutorial
https://www.wpbeginner.com/plugins/how-to-deactivate-all-plugins-when-not-able-to-access-wp-admin/