You can have several Photos Libraries. You just have to name them differently to keep them apart.
Using multiple Photos Libraries is explained on this Help page, see: Create additional photo libraries in Photos on Mac - Apple Support
To create a new library for iCloud,
- launch Photos while holding down the options key ⌥. Keep holding down this key until the Library Chooser dialog appears.
- Select "new" to create a different library. Give it a different name from your main Desktop Library.
To make the new library your iCloud Library see this page: Use iCloud Photos to store photos in iCloud - Apple Support
- While browsing the new library: First open the Photos > Preferences > General and click "Use as System Photo Library", because only the System Photos Library can sync with iCloud.
- If you’re not already signed in to iCloud, choose Apple menu > System Preferences, then click iCloud and sign in with your Apple ID and password.
- In the Photos app on your Mac, choose Photos > Preferences, then click iCloud.
- Select the iCloud Photos checkbox.
To switch between your Libraries, double click the library in the Finder that you want to open in Photos.