While there has been an update for the standalone extension (compatible with TYPO3 v8) https://extensions.typo3.org/extension/rtehtmlarea/ and a TYPO3 7 ELTS release, you might be in the unlucky position that your version 8 upgrade is "just in progress" and the issue hits you hard.
For those who need a quick fix we provide the fix in multiple ways:
See the change on github
https://github.com/liayn/TYPO3.CMS/commit/15b240d849656e56b0543a645cd3e9b4345af6d5 (Updated for Chrome 91!)
Cherry-pick the change
If you are running your TYPO3 straight from a git checkout, you can simply cherry-pick the change:
git fetch "https://github.com/liayn/TYPO3.CMS.git" TYPO3_7-6 && git cherry-pick FETCH_HEAD
Apply the patch manually
Download the patch file to your server and apply the fix manually:
patch -p0 < Make_rtehtmleditor__RTE__compatible_with_Chrome_91.patch
Apply the patch via composer
First, install the
composer require cweagans/composer-patches
Then, copy the patch file provided below into
patches/rte.patch of your composer installation.
Finally, add this part to your
"fix rte": "patches/rte.patch"
Note: This fix is only a work around to help you out quickly. We strongly advise to upgrade your TYPO3 to version 8 LTS or higher as soon as possible.
This information applies to TYPO3 7 LTS