[BUG] FlexForm settings are not read in controller classes

[beatrycze-volk]

Description

The settings array should contain settings from FlexForm but instead it contains only configuration from TypoScript.

Reproduction

See: #1298

Expected Behavior

Settings from FlexForms should be available inside the controller classes.

Screenshots and Examples

See: #1298

Environment

See: #1298

Additional Context

Currently two counter measures are introduced but they only mask the error instead of fix it:

• [BUGFIX] Check if array is not null before checking for the existence of the key #1322
• [MAINTENANCE] Sanitize settings from FlexForm #1324

Probably bug was introduced during the update to TYPO3 11.x.