Magento 2.3 product attribute and ui component

First, I created the UI component: Vendor/Module/view/adminhtml/ui_component/product_form.xml

<form xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Ui:etc/ui_configuration.xsd">     <fieldset name="product-details">        <container name="fieldname_container">            <argument name="data" xsi:type="array">                <item name="config" xsi:type="array">                    <item name="sortOrder" xsi:type="number">160</item>                </item>            </argument>            <field name="fieldname" formElement="multiselect">                <argument name="data" xsi:type="array">                    <item name="config" xsi:type="array">                         <item name="dataScope" xsi:type="string">fieldname</item>                         <item name="filterOptions" xsi:type="boolean">true</item>                         <item name="showCheckbox" xsi:type="boolean">true</item>                         <item name="disableLabel" xsi:type="boolean">false</item>                         <item name="multiple" xsi:type="boolean">true</item>                    </item>                </argument>                <settings>                    <validation>                        <rule name="validate-field" xsi:type="boolean">true</rule>                    </validation>                    <dataType>varchar</dataType>                    <label translate="true">Field label</label>                    <dataScope>fieldname</dataScope>                </settings>                <formElements>                    <multiselect>                        <settings>                            <options class="Vendor\Module\Model\Backend\Product\Source\FieldName"/>                        </settings>                    </multiselect>                </formElements>            </field>        </container>    </fieldset> </form> 

however when I save product the values of the custom attribute are not saved.

Created attribute and added it to product but now I have that field twice in product form. ( values are being saved )

If I remove created field from attribute set values are not being saved.

what is wrong here ?