I have a project server farm 2016, I need to only copy projects with its project site (about 100 projects) from my old farm 2013 to the new farm
I don't want to do full migration, only Enterprise projects with sites need to copy it?
Unfortunately, there is no straightforward way to achieve your goal!
You have two options:
Boring Manually Option
Microsoft Project.Migration Option
Note: this option will lead to removing all settings that have been implemented in Project Server 2016 like Permission Settings, New Lists, sites, current projects...etc
Check also Install and configure Project Server 2016.