Getting the List of all sites/ sub-sites and their owners using PnP

Did you try using Search webpart or Search REST API

You can use search with either the Search Web Parts or using REST for search.

Search WebPart:

   Find all Site Collections:    “contentclass=STS_Site”
   Find all Webs (top level sites and subsites):    “contentclass=STS_Web”

  http://techtrainingnotes.blogspot.com/2015/07/using-sharepoint-serach-to-find-sites.html

Search REST API:

   http://yourserver/sites/yoursite/_api/search/query?querytext='contentclass=STS_Site'
   http://yourserver/sites/yoursite/_api/search/query?querytext='contentclass=STS_Web'

  https://msdn.microsoft.com/en-us/library/office/jj163876.aspx

You could also use Graph API to get these details

https://www.c-sharpcorner.com/article/retrieve-site-collections-and-subsites-using-microsoft-graph-api/

Owner for each site can be fetched using

https://graph.microsoft.com/beta/sites/{site-id}?$select=*,drive&$expand=drive