Any backup location is secure as long as you encrypt your data securely before you back it up there.

For something as important as a backup thag you don’t want to lose, I’d stick with something tried and true like Backblaze B2.

Backblaze is also very cheap for what it is (a great storage solution). You can pay monthly or use more of the regular pay as you go model.

Monthly and pay as you go have ups and downs, but the benefit of pay as you go for me is the ridiculously cheap deal (if you download your backups a lot it may be less so, but I don’t so it works out very cheap for me).