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 User Settings¶
You might consider clearing the Backend user preferences. This can avoid problems, if something in the upgrade requires this. Go to "Clean up", scroll to "Reset user preferences" and click "Reset backend user preferences".