Updated 2024-10-12
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 (availabel as Beta) with rclone and iCD.
So while waiting for a free working version I solved my sync between iCD and MBA with Syncthing(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.