TYPO3 - How to display form in grid element?

I use TYPO3 v10.4.8 with the extension gridelements and the core form extension. I have included the form into my created grid element in the backend, but it's not visible in frontend. This is a part of my grid template:

<f:if condition="{children}">
    <f:for each="{children}" as="columns" key="rowNumber">
        <div class="row grid-row grid-row-{rowNumber}">
            <f:if condition="{columns}">
                <f:for each="{columns}" as="column" key="columnNumber">
                    <div class="col-12 grid-column grid-column-{columnNumber}">
                        <f:for each="{column}" as="child">
                            <div class="inner">
                                <f:cObject typoscriptObjectPath="tt_content.{child.data.CType}" data="{child.data}" table="tt_content" />
                            </div>
                        </f:for>
                    </div>
                </f:for>
            </f:if>
        </div>
    </f:for>
</f:if>

My configuration:

lib.gridelements.defaultGridSetup =< lib.contentElement
lib.gridelements.defaultGridSetup {
    templateName.field = tx_gridelements_backend_layout
    templateName.ifEmpty = GridElement
  layoutRootPaths {
    10 = EXT:gridelements/Resources/Private/Layouts/
    20 = {$page.fluidtemplate.templateRootPath}
  }
  partialRootPaths {
    10 = EXT:gridelements/Resources/Private/Partials/
    20 = {$page.fluidtemplate.templateRootPath}
  }
  templateRootPaths {
    10 = EXT:gridelements/Resources/Private/Templates/
    20 = {$page.fluidtemplate.templateRootPath}
  }
  dataProcessing {
    10 = GridElementsTeam\Gridelements\DataProcessing\GridChildrenProcessor
    10 {
      default {
        as = children
        options {
            resolveChildFlexFormData = 0
        }
      }
    }
  }
}

The Render.html file from the core module is called, but the variable formConfiguration is empty, so no form is rendered.

Solution

Since a form element uses the pi_flexform field to select the form definition, you have to disable the automatic FlexForm resolver of Gridelements.

By default Gridelements with dataProcessing is meant to be rendering everything within a FLUID template by accessing variables and settings directly. So the default setting of the DataProcessor is to resolve FlexForm XML data into arrays.

To disable that behaviour you can use the option

resolveFlexFormData = 0

to disable it for a container and its children or

resolveChildFlexFormData = 0

to still resolve container FlexForms but skip those of child elements.