Hm, but wouldn’t it be possible to setup a VPS to do tun duplicati in the clould (i.e. without downloading and reuploading it to your local computer)? Like this cloud-to-cloud migration scenario, except that you run duplicati instead of rclone?
Not sure if it’s worth the hassle and the cost for the VPS, but possible it is, no?
An alternative (not linked to duplicati at all) would be pcloud. If you have pcloud storage (10 GB free) you can make it backup various cloud drives like dropbox and google drive. Without the need of any other software. (Disclaimer: the link to pcloud is an affiliate link)