Duplicati is an open source, free to use application, that can be used to make backups to a large set of storage providers.
Some time ago, I was looking for a program to allow me to backup my data to an online storage host like Backblaze or Google Cloud. I first came across CloudBerry (https://www.cloudberrylab.com/) and downloaded their trial software. At a first glance, it was OK but it had one major downside which I come to next and that many people seem to forget when comparing backup solutions.
Only under the condition that my data is encrypted, am I willing to backup sensitive information, like photo albums, documents and what not to an external cloud provider. Both Duplicati and CloudBerry (and also many other clients for that matter) support encryption. Why is encryption important? It prevents unauthorized users or companies to look in my data. The prevention is based on the mathematical (or better yet computational) difficulty to decrypt data without the only-to-me-known key.
The statement holds also in the other direction in the following sense: Important is that the safety of data is only based on this one-way trap door. In particular, the code responsible to encrypt my data should be known, open and verifiable to me and others. If a product that encrypts and stores data, trust resides in the correct functioning of encryption. Instead of trust I prefer the rely only on the underlying principles of encryption.
In fact, I would go as far as that any software that encrypts data should be open source and readable to anyone.
Coming back to where I left off and taking this precondition into account, Duplicati is an excellent candidate to rely on for making backups. Besides that, it has an active community and is actively maintained and developed.