The configuration for a preview publishing target database along with a site definition, to be put under App_Config\Include folder

PreviewPublishingTarget.config

<?xml version="1.0" encoding="utf-8" ?>
<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/">

  <!--
  
  This configuration adds "preview" publishing target as a copy of production-like "web" database for Sitecore 9.3
  Please refer to a full guide video for the usage instructions: https://youtu.be/...

  WARNING!
  This configuration is done for demo purposes only, do not use it as is.
  Please split it into relevant configuration patches under appropriate Helix modules when applying on your real solution
  
  -->

  <sitecore>
    <sites>
      <site patch:before="*[@name='website']"
            name="preview" 
            scheme="https"
            hostName="preview.digitalecosystem.local"
            targetHostName="preview.digitalecosystem.local"
            enableTracking="true"
            virtualFolder="/"
            physicalFolder="/"
            rootPath="/sitecore/content"
            startItem="/Home"
            language="en"
            database="preview"
            domain="extranet"
            allowDebug="true"
            cacheHtml="false"
            htmlCacheSize="50MB"
            registryCacheSize="0"
            viewStateCacheSize="0"
            xslCacheSize="25MB"
            filteredItemsCacheSize="10MB"
            enablePreview="true"
            enableWebEdit="true"
            enableDebugger="true"
            disableClientData="false"
            cacheRenderingParameters="false"
            renderingParametersCacheSize="10MB"
            enableItemLanguageFallback="false"
            enableFieldLanguageFallback="false" />
    </sites>
    <databases>
      <database id="preview" patch:after="database[@id='web']" singleInstance="true" type="Sitecore.Data.DefaultDatabase, Sitecore.Kernel">
        <param desc="name">$(id)</param>
        <icon>Images/database_web.png</icon>
        <securityEnabled>true</securityEnabled>
        <dataProviders hint="list:AddDataProvider">
          <dataProvider ref="dataProviders/main" param1="$(id)">
            <disableGroup>publishing</disableGroup>
            <prefetch hint="raw:AddPrefetch">
              <sc.include file="/App_Config/Prefetch/Common.config" />
              <sc.include file="/App_Config/Prefetch/Webdb.config" />
            </prefetch>
          </dataProvider>
        </dataProviders>
        <PropertyStore ref="PropertyStoreProvider/store[@name='$(id)']" />
        <remoteEvents.EventQueue>
          <obj ref="eventing/eventQueueProvider/eventQueue[@name='$(id)']" />
        </remoteEvents.EventQueue>
        <archives hint="raw:AddArchive">
          <archive name="archive" />
          <archive name="recyclebin" />
        </archives>
        <cacheSizes hint="setting">
          <data>100MB</data>
          <items>50MB</items>
          <paths>2500KB</paths>
          <itempaths>50MB</itempaths>
          <standardValues>2500KB</standardValues>
        </cacheSizes>
        <BlobStorage hint="raw:AddBlobStorage">
          <providers default="classic">
            <provider name="classic" type="Sitecore.Data.Blobs.ClassicSqlBlobProvider, Sitecore.Kernel">
              <param desc="databaseName">$(id)</param>
            </provider>
          </providers>
        </BlobStorage>
      </database>
    </databases>
    <eventing defaultProvider="sitecore">
      <eventQueueProvider defaultEventQueue="core">
        <eventQueue name="preview" patch:after="eventQueue[@name='web']" type="Sitecore.Data.Eventing.$(database)EventQueue, Sitecore.Kernel">
          <param ref="dataApis/dataApi[@name='$(database)']" param1="$(name)" />
          <param hint="" ref="PropertyStoreProvider/store[@name='$(name)']" />
        </eventQueue>
      </eventQueueProvider>
    </eventing>
    <PropertyStoreProvider defaultStore="core">
      <store name="preview" patch:after="store[@name='web']" prefix="preview" getValueWithoutPrefix="true" singleInstance="true" type="Sitecore.Data.Properties.$(database)PropertyStore, Sitecore.Kernel">
        <param ref="dataApis/dataApi[@name='$(database)']" param1="$(name)" />
        <param resolve="true" type="Sitecore.Abstractions.BaseEventManager, Sitecore.Kernel" />
        <param resolve="true" type="Sitecore.Abstractions.BaseCacheManager, Sitecore.Kernel" />
      </store>
    </PropertyStoreProvider>
  </sitecore>
</configuration>