We are using SharePoint Modern communication site on SharePoint Server 2019. I am tasked with customizing the out-of-the-box template for header and adding a footer. I was toying with using https://github.com/pnp/sp-dev-fx-extensions/tree/main/samples/react-application-injectcss but I am unable to get it to work.
The SPPKG file throws the following error when I deploy it to SharePoint Server 2019 apps. How do I modify the look and feel of Communication Site header in SharePoint 2019. Any help would be appreciated.
There were errors when validating the App manifest.:Xml Validation Exception: 'The 'IsDomainIsolated' attribute is not declared.' on line '1', position '322'.