Usage statistics for Duplicati Backend stats show SSH (SFTP) is the number two backend behind File, although I’m sure some of that is local not offsite. SFTP servers exist for Windows too, and many NAS systems also have it. Even though it’s easy to get, FTP over the Internet is not secure (clear-text login). FTPS (FTP secured with SSL/TLS) and WebDAV are also possibilities for building something yourself. Setting up self-hosted Minio on Windows 10 with automatically renewing SSL certificate is S3 protocol.
Backing up 10 TB might be pushing capacity limits (after some versions) for a single drive these days, however if you want something easier on the electric bill than a PC-based server, a single-bay NAS for about a hundred dollars plus drive might work. You won’t get drive redundancy, but maybe that’s OK…