TYPO3 Core

While trying to perform an upgrade to the latest version of TYPO3 9 LTS (i.e. from 9.5.17 to 9.5.19) I received the following message when trying to update the core from the backend (Admin tools -> Upgrade -> Update core):
"To perform an update, the folder structure of this TYPO3 CMS instance must stick to the conventions, or the update process could lead to unexpected results and may be hazardous to your system,
"Automatic TYPO3 CMS core update not possible: Folder structure has errors or warnings".

I'd suggest to add the hint to this message that you should go to "Admin tools -> environment" and "Check directory status" to fix this error.
I always find it a bit annoying when you receive an error without any hints what to do now. In this case it's really easy to give an advice to the user what to do.

(Actually, I could imagine that Checking/Fixing the directory status will be directly offered as an instant action or even automagically executed internally. In my case, updating the core was not possible because the index.html file was not present in typo3temp, though typo3temp was writable for the www-user. Imo no reason to prevent the update from successfully executing...)