With my project to keep a MacBook Air 2011(MBA) alive, Ubuntu installed, i searched for a solution where my iCoud drive(iCD) was continuous synced with my MBA. This must work both ways so even a file change made on MBA should be replicated to iCD.
There is MultCloud, are there others ?, but the free version is just 5 Gb data traffic per month. There is also a work in progress ? with rclone and iCD.
So while waiting for a free working version I solved my sync between iCD and MBA with Syncyhing(ST). ST doesn't sync with iCloud so the work around here was to use my MacMini, Mac OS, as the "Middle man". It's always on and synced with iCD.