It seems a wiered requirement that you need a login on aem publisher for serving the content. normally Aem publisher has anonymous user that has permission for /content and /etc.clientlibs to serve the pages, assets and clientlibs anonymously without requiring you to login and dispatcher will severs...

What was the prior version of aem service pack before installing sp16?

Hope this helps  /jcr:root/content//element(*,cq:Page)[(@cq:lastModified >= xs:dateTime('2023-10-25T04:00:00.000-05:00')  You can change the date as per your requirements 

Not sure about your use case but you can clearly use the query to find all href authored on your page either via full text query. I don’t have query ready for you but you can surely read this article to know more about full text query in aem https://sourcedcode.com/blog/aem/find-aem-jcr-nodes-with-f...

Sitemap.xml is generated dynamically and might be stored on your dispatcher cache. Can you check if you are seeing the cached sitemap.xml. Also, check  Sitemap scheduler OSGi configuration to check the cron expression for the frequency. https://experienceleague.adobe.com/docs/experience-manager-lear...

If you want the redirect url to be updated in url as well then you should be using sendRedirect() method of the servlet. Read this article to know more https://www.javatpoint.com/sendRedirect()-method#:~:text=Difference%20between%20forward()%20and%20sendRedirect()%20method&text=The%20forward()%20met...

I believe excerpt will only work with full text indexed property and not with synonyms. Synonyms words will only tell aem to also look for the configured synonyms word to search for.  

There are various ways to achieve the automation of dispatcher flush Curl command https://experienceleaguecommunities.adobe.com/t5/adobe-experience-manager/dispatcher-cache-clear-by-curl-script/m-p/212350acs-commons(on-demand manually): https://adobe-consulting-services.github.io/acs-aem-commons/fea...

I believe Workflow in brand portal is not customizable. Pleas open an adobe support ticket to confirm this 

I believe your client lib get updated with new code drop and after code drop you don’t see the updated versioned client libs on your dispatcher means your dispatcher is still caching the old cache. So, probably you need a dispatcher flush with each code drop. You can either automate it via a script ...