Borgbase. I'm not affiliated with them, I'm just a happy customer
Pretty much anyone you can pay to host a database, you can pay to back it up. Amazon rds, heroku postgres, google cloud sql... pick the service that works for you, and they have some affordance for backups. Backups are something I expect, rather than something I shop around for.
My experience says to backup to a different vendor.
This is part of my threat model. Is there an easy way to do this with e.g. hosted RDS or block storage device snapshots?
In my case I'm dumping + zipping the entire database at the application level. In my case is as simple as adding a library [1], scheduling the job and transferring to AWS S3 (my main application is on DigitalOcean)