TYPO3 9.5.7 / Extbase: Add wizard in flexform

Question

I'm trying to add the 'add wizard' in my flexform of my extension, but the add button doesn't show up. The flexform itself is working by the way. I want to give the backend users the possibility to add new items from the plugin configuration. ps: Reinstalled the extension, cleared all the caches... My flexform:

<T3DataStructure>
<sheets>
    <sDEF>
        <ROOT>
            <TCEforms>
                <sheetTitle>Viewer Configuration</sheetTitle>
            </TCEforms>
            <type>array</type>
            <el>
                <settings.viewer>
                    <TCEforms>
                        <label>Viewer select</label>
                        <config>
                            <type>select</type>
                            <renderType>selectSingle</renderType>
                            <size>1</size>
                            <minitems>0</minitems>
                            <maxitems>1</maxitems>
                            <foreign_table>tx_myext_domain_model_viewer</foreign_table>
                            <foreign_table_where>AND tx_myext_domain_model_viewer.deleted = 0 AND tx_myext_domain_model_viewer.hidden = 0 AND tx_myext_domain_model_viewer.pid = ###CURRENT_PID### ORDER BY tx_myext_domain_model_viewer.name</foreign_table_where>
                            <wizards>
                                <add>
                                    <type>script</type>
                                    <title>Create</title>
                                    <icon>EXT:backend/Resources/Public/Images/FormFieldWizard/wizard_add.gif</icon>
                                    <params>
                                        <table>tx_myext_domain_model_viewer</table>
                                        <setValue>set</setValue>
                                        <pid>###CURRENT_PID###</pid>
                                    </params>
                                    <module>
                                        <name>wizard_add</name>
                                    </module>
                                </add>
                            </wizards>
                        </config>
                    </TCEforms>
                </settings.viewer>
            </el>
        </ROOT>
    </sDEF>
</sheets>
</T3DataStructure>

Answer 1

It is indeed still impossible with selectSingle renderType. There is also a new ticket in bugtracker about it here:

https://forge.typo3.org/issues/81976

It is 19 days old and there is already a fix by the looks of it.