SOLIDWORKS 2020 provides you with the capability of saving a copy of a part or an assembly with a subset of its configurations. This will save time by not having to delete the configurations manually afterwards.
When selecting configurations to save, the active configuration is selected by default. Also, if you select a derived configuration, its parent configuration is selected as well. It is interesting that linked display states will remain in the copied model.
To save as a copy with a subset of configuration, open a model, right-click on a configuration in the Configuration Manager, and choose Save Configurations.
In the Save Configurations as a new Assembly/Part dialog box, select the desired configurations by checking the box next to their names. You can also select all the configurations by clicking on the Save Icon at the top of the column.
Once everything is selected, click on Save Selected. This will allow you to browse to the location where you want to save your copied assembly file.