A collegue reported the same exception with a slichtly different scenario. A normal
editor adding a page beneath a siteroot, but the site-config yaml file is missing.
The DataHandler for new records(page) adds for TCA managed tables, if they have a
languageField configuerd the languageField data if a) a site config can be loaded
and b) the current backend user has a matching/allowed siteLanguage in it. If not,
nothing is done (in earlier version there was a fallback for all siteconfig which
has been removed).
That means, if no SiteConfig can be found the recordEditAccesInternals fails for
new records.
In case of the sysfolder scenario on root page, that is the same issue as no siteconfig
can be found (uid = 0 has no siteconfig).
Need to talk with some people how the overall plan is, and if a "siteconfig" should be
required for ALL root-level things and how to deal when adding something on root-level.
Eventually the "root-level" is considerd as "admin only".
For my collegue it was easy to simply provide the siteconfig yaml file for the siteroot in
the rootline and the error was gone.
Note: Having sysfolders on rootlevel without a siteconfig as parent in the rootline does
not work for multi-language sites - so maybe consider to create the sysfolder beneath a
site - albeit not tackling this issue directly.
I'd say this nees deeper thinking and (finally) a concept how that level should work and
if a siteconfig should be required for lowest points or not.
Issue #98262 also states this in a comment:
Update, in case anyone stumbles upon this page googling the error message: it turns out editors cannot create pages outside of web roots in Typo3 11 (and perhaps 10 - noticed this after upgrading from 9 to 10 and subsequently to 11). I had a tree of maps containing address records outside the root of a website. Have now moved that inside and editors are able to add maps again. Strange behaviour in my opinion, as the editor should have access according to the access module.
that normal editors are not allowed to create pages outsite of a valid webroot (siteroot/having a siteconfig).
The point is, that it needs to made clear if that is the wanted behaviour or not, and either properly documented
or guarded EARLIER (not allowing to start creating it on the rootlevel/outsite a webroot) etc.