I store my documents in I-cloud.

Time Machine will only backup things that have a local copy on your Mac.

If you don't have Optimize Mac Storage turned on at Apple menu > System Preferences > Apple ID > iCloud then your documents will have a local copy. If you don't have Optimize Mac Storage turned on at Photos app > Photos menu > Preferences > iCloud then your photos will have a local copy.

If you do have those options turned on then some or all of your documents and photos may not have a local copy and would not be included in a Time Machine backup.

More information on those Optimize options is in: Add your Desktop and Documents files to iCloud Drive - Apple Support and Set up and use iCloud Photos - Apple Support

If the only copy is in iCloud (i.e., there is no local copy) there is no way to back them up. You are relying on Apple. The following has information that may help, but it isn't about backing up directly from iCloud. Archive or make copies of the information you store in iCloud - Apple Support