Currently, there is no tool to copy geometry and insert them between two feature layers in ArcGIS Online. Although copying geometry from one feature layer and adding it to another is not possible, there are options to copy the items and contents, which allows for duplication of geometries while retaining the attributes and features in ArcGIS Online.
Copy the item in ArcGIS Online using ArcGIS API for Python
Web maps, configurable apps, dashboards, shapefiles, file geodatabases, and other items can be copied in ArcGIS Online using ArcGIS API for Python. Refer to the article, How To: Copy/clone content from one ArcGIS Online organization or Portal for ArcGIS to another for instructions.
Create a feature template in ArcGIS Pro before publishing it in ArcGIS Online
Creating a feature template in ArcGIS Pro allows the owner to have a default template that can be used or published multiple times in ArcGIS Online with no changes affecting it. Refer to ArcGIS Pro: Create a feature template for more information.
Copy the feature’s attributes and shape in ArcGIS Field Maps
Copy the feature’s attributes and shape and add them to a new feature in ArcGIS Field Maps. Refer to ArcGIS Field Maps: By copying an existing asset or observation for more information.