These menu entries are disabled when the content is not editable (eg. if the package content is sealed, or when the used logged in the vRO client has no 'Edit' permission).
Thank you for your answer. The user in the vRO client is a member of 'Admin group' "vsphere.local\Administrators"
In vRO clients V7.4 und V7.5 same user (and same SSO server) is used, but this problem doesn't occur.
I changed the line
in the corresponding pom.xml file '...\o11nplugin--package\pom.xml', and installed it on vRO V7.6, but the menu entries (like "Rebuild package", "Delete...", "Edit", ...) remain disabled.
Thank you for your support.