Error: plug ins declaring extensions or extension points must set the singleton directive to true

In the use of eclipse When developing plug-ins , An error occurred during operation ：Plug-ins declaring extensions or extension points must set the singleton directive to true, That is, if the following screenshot appears ：

Only need to MANIFEST.MF in

Manifest-Version: 1.0
Bundle-ManifestVersion: 2
Bundle-Name: Myplugin2
Bundle-SymbolicName: Myplugin2
Bundle-Version: 1.0.0.qualifier
Automatic-Module-Name: Myplugin2
Bundle-RequiredExecutionEnvironment: JavaSE-17
Import-Package: org.eclipse.ui
Require-Bundle: org.eclipse.jface

Which line of the error report is added " ; singleton:=true" That's all right. .

Manifest-Version: 1.0
Bundle-ManifestVersion: 2
Bundle-Name: Myplugin2
Bundle-SymbolicName: Myplugin2;singleton:=true
Bundle-Version: 1.0.0.qualifier
Automatic-Module-Name: Myplugin2
Bundle-RequiredExecutionEnvironment: JavaSE-17
Import-Package: org.eclipse.ui
Require-Bundle: org.eclipse.jface

If you add it, you won't report an error , As shown in the figure below ：