how can I delete photos from only one device, but leave them in icloud?

See the "How do I turn off iCloud Photos on only one device?" section of Get help with iCloud Photos - Apple Support

Note that it means that you are turning off iCloud Photos on that device and that if you ever turn it back on, they will sync back to it.

When photo library is set up in photo application of Mac https://support.apple.com/en-in/HT204264

And preferences is set up https://support.apple.com/en-in/guide/photos/pht5156cc968/4.0/mac/10.14

According to it - Preference

Explanation

iCloud Photos

Select the tickbox to turn on iCloud Photos.

If you uncheck the box of iCloud photos in photo preferences , open photos application and also sign in with Apple ID and password at www.icloud.com , when you right click on a photo in system photo library folder of Mac and delete it , it will be deleted from the photo application and moved to recently deleted folder and kept for 30 days both in iCloud.com / and photo application .

The photo will be deleted from the application but still visible in iCloud.com

In the screen shot I have deleted a photo " true " .

This is for a single photo , for selected photos if photos are in continuous series , hold shift key and click on the first photo and then the last photo to get selected ( suppose there are 100 photos , you have to click on 80 th photo , the rest of 20 photos will not be selected , its an example to explain only ) , and then right click on them and delete them .