As stated in PnP GitHub page (https://pnp.github.io/):
These assets are created and maintained by Microsoft & the community
The Community (also known as the PnP community) is an open-source initiative coordinated by Microsoft engineering.
PnP uses supported and recommended techniques defined by Microsoft
This community contributes to development documentation, samples, reusable controls, and other relevant open-source initiatives related to Microsoft 365 usage and development.
PnP isn't a product
Therefore it is not supported by official support channels. If the experienced issue(s) is caused by out-of-the-box API, it falls on the normal support patterns from Microsoft side.
PnP libraries are open source Community efforts to share reusable "tools" in order to simplify day-by-day development.
If you want a complete reference of all type of development API available on SharePoint you can check the SharePoint APIs official documentation (https://learn.microsoft.com/en-us/sharepoint/dev/sp-add-ins/sharepoint-net-server-csom-jsom-and-rest-api-index)
If you prefer not to use PnP.Core, and you are going to use only SharePoint Online, probably the most suitable options you have are:
For some tasks, like one-time sites configuration, or batch activities, I often suggest PnP PowerShell Module (https://github.com/pnp/powershell).