Can't activate StoragePoint Modern UI (SPFx Extension) in SharePoint 2019 (4274441)

• Can't activate StoragePoint Modern UI (SPFx Extension) in SharePoint 2019.
• Unexpected error occurred while activating feature behind SharePoint Framework (SPFx).

Error: System.Exception: Feature behind SPFx Extension cannot be activated, SharePoint App Services and AppCatalog for the Web Application 'SharePoint - infoworld-test' are not configured properly. at Bluethread.SharePoint.StoragePoint.FeatureSPFxExtension.a(SPSite A_0) at Bluethread.SharePoint.StoragePoint.FeatureSPFxExtension.a.b() at Microsoft.SharePoint.Utilities.SecurityContext.RunAsProcess(CodeToRunElevated secureCode) at Microsoft.SharePoint.SPSecurity.RunWithElevatedPrivileges(WaitCallback secureCode, Object param) at Microsoft.SharePoint.SPSecurity.RunWithElevatedPrivileges(CodeToRunElevated secureCode) at Bluethread.SharePoint.StoragePoint.FeatureSPFxExtension.FeatureActivated(SPFeatureReceiverProperties properties) 9- 5 PM India time (GMT+5:30)

• App manifest schema file in "C:\Program Files\Common Files\microsoft shared\Web Server Extensions\16\TEMPLATE\XML\appmanifest.xsd" was incorrectly updated.
• This issue happens when user cannot deploy StoragePoint Modern UI package during profile creation/update and the following "App Deployment" verbose log is present in ULS logs:

SharePoint Foundation    App Deployment    Verbose    App Packaging: Validating XML file stream.

SharePoint Foundation    App Deployment    Verbose    App Packaging: Appmanifest XML Validation error thrown: Xml Validation Exception: 'The 'IsClientSideSolution' attribute is not declared.' on line '1', position '249'.   

SharePoint Foundation    App Deployment    Verbose    App Packaging: Appmanifest XML Validation error thrown: Xml Validation Exception: 'The element 'Properties' in namespace 'http://schemas.microsoft.com/sharepoint/2012/app/manifest' has incomplete content. List of possible elements expected: 'StartPage' in namespace 'http://schemas.microsoft.com/sharepoint/2012/app/manifest'.' on line '1', position '338'.   

SharePoint Foundation    App Deployment    Verbose    App Packaging: Appmanifest XML Validation error thrown: Xml Validation Exception: 'The element 'App' in namespace 'http://schemas.microsoft.com/sharepoint/2012/app/manifest' has incomplete content. List of possible elements expected: 'AppPrincipal' in namespace 'http://schemas.microsoft.com/sharepoint/2012/app/manifest'.' on line '1', position '351'.

• Please backup the current XML schema file and to replace it with the App manifest XML schema file below in "C:\Program Files\Common Files\microsoft shared\Web Server Extensions\16\TEMPLATE\XML\appmanifest.xsd".
• This App manifest XML schema file below is valid manu RTM versions on top of SharePoint 2019 RTM version (16.0.10337.12109).
• It is important to do that on all SharePoint servers in SharePoint farm.

Reference