TYPO3 SiteConfiguration uses pseudo TCA, or better to say, a
restricted subset of usual TCA to provide form engine based
backend module editing cababilities.
Thus, TCA/FormEngine uses table as it does not know that it
sources site configuration stuff from files instead of database
tables.
Taking the rest of the error message, I assume that you have a
forceLanguage:
key in one of the site configuration yaml fields, which does not have a valid pseudo tca for it.
Did you used 3rd party extensions adding custom configuration to the
site configuation tca and removed it during the update ? Eventually,
that extension has an update.
If that was done by a custom local project extension or sitepackage
extension, ensure that the syntax is still correct and loaded.
Otherwise, search for that file in the site-configuration files manually.
when accessing any site configuration in the backend:
That helps you to look directly into that specific site which is crushing
and remove the invalid value - or determine which has defined that pseudo
code.
Just to be sure, did you executed all TYPO3 upgrade wizards already ?
TYPO3 v11 does not defines that SiteConfiguration field at all, so it must be something custom or introduced by a 3rd party extension. Check all installed extension if a Configuration/SiteConfiguration folder exists
with some content - and lookup which defines the forceLanguage field.
Reading the message again, it seams that not the key forceLanguages is the issue, but the value:
forceLanguages: language
or similar. Comment that out, clear all caches and you should be able to open the site config in the backend (except there are further error based of the extending)
