dears i works on Branch version with ArcGIS Pro 2.9.1 & Enterprise 10.9.1, SQL Server 2017 Enterprise.
Also ESRI says that private versions are only accessible by the version owner and VMS admin so no one else can see private versions or even know they exist.
BUT, in my case i access Portal from ArcGIS Pro with Editor user type and Viewer role and the user could see these Private versions which created by portaladmin user.