Selecting photos in iCloud.com

Yes you can—just hold down the Command key as you click on photos to select. You can then click on the Trash icon to delete them all in one go.

You can also try selecting a moment, then click the Share button, and then cancelling the Share. The photos should remain selected.

Keep on holding command key and tap the photos to get them selected , to delete them at once click on delete key on the keyboard .

You are welcome. I read a post where someone who is very experienced in Photos/iCloud Photos suggested it.