TYPO3 v9 has reached its end-of-life September 30th, 2021 and is not maintained by the community anymore. Looking for a stable version? Use the version switch on the top left.

You can order Extended Long Term Support (ELTS) here: TYPO3 ELTS.

Clear Caches

You should also clear all caches when upgrading.

Go to "Maintenance" and click "Flush":

Flush Caches

The option "Flush" in the Install Tool.

Additionally, after an upgrade to a new major version, you should also delete the other temporary files, which TYPO3 saves in typo3temp/. In the Install Tool go to "Clean up" to do so.

Remove temporary assets.

The option "Remove temporary assets" in the Install Tool.