RichTextAreaComponent.design

<design:component>
    <design:attribute name="value" description="The value for RichText Area Component"/>
    <design:attribute name="label" description="The Label for RichText Area Component"/>
    <design:attribute name="required" description="Input is required or not value should be true or false"/>
    <design:attribute name="placeholder" description="The place holder"/>
</design:component>

RichTextAreaComponent.html

<aura:component implements="lightning:availableForFlowScreens" >
    
    <!-- Attributes -->
    <aura:attribute name="value" type="String" />
    <aura:attribute name="label" type="String" />
    <aura:attribute name="required" type="Boolean" />
    <aura:attribute name="placeholder" type="String" />
    
    <!-- Handlers -->
    <aura:handler name="init" value="{!this}" action="{!c.doInit}"/>
    <aura:attribute name="validate" type="Aura.Action"/>
    <!-- 
      isValid = true/false
      errorMessage - 
    -->
    
    <lightning:inputRichText labelVisible="true" 
                             label="{!v.label}"
                             required="{!v.required}"
                             variant="bottom-toolbar" 
                             value="{!v.value}" 
                             placeholder="{!v.placeholder}">
        <lightning:insertImageButton/>
    </lightning:inputRichText>
</aura:component>

RichTextAreaComponentController.js

({
    doInit : function(component, event, helper) {
        var error = 'Please complete required information.';
        component.set('v.validate', function() { 
            if( component.get("v.required") && !component.get("v.value") ) {
                return { 
                    isValid: false, 
                    errorMessage: error 
                }
            }else{
                return { 
                    isValid: true, 
                    errorMessage: error 
                }
            }        
        });
    }
})