The most common reason to need a backup.
IMMEDIATE ACTION
If you took a backup before updating, restore it. That is why you took it, and it is faster than diagnosing.
IF YOU DID NOT
Identify what broke. Check cPanel > Metrics > Errors, and the application's own log.
Usually the update itself, an incompatibility between an extension and the new core version, or a PHP version problem.
DISABLING THE CULPRIT
Rename the plugin or extension directory through File Manager. That disables it without needing to log in.
If the site returns, you have identified the problem.
RESTORING PARTIALLY
Restore only the updated component from your backup rather than the whole site. Less disruptive, and it preserves content added since.
IF THE DATABASE WAS UPDATED
Some updates change the database schema. Restoring old files with an updated database produces errors.
In that case restore both from the same date.
PREVENTING RECURRENCE
Back up before every update Update a few items at a time so the culprit is identifiable Test major updates on staging
