Backups and even accessing files can be a bit of a pain with two OS. NTFS drivers for Linux are a thing and they mostly work but I would not overly rely on it. For this reason, I would consider using a NAS for storing and accessing your files. It can also handle your backups with Rclone.
Data Hoarder
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As it was said, the best option is to have separate storage for backups, ideally backup NAS. IT will also give additional protection and would help you to fit 3-2-1 backup rule. As for encryption, rclone should handle this. Alternatively, you may check starwinds vtl with backup software, cloud provider won't be able to access the data stored inside of the virtual tape, but you should check if it works with google drive.