If you are looking for a synced folder similar to Dropbox, I would recommend Tresorit. Files are always end-to-end encrypted and they operate as a highly trustworthy Swiss company. The downside is a relatively high price compared to the providers that are not as privacy-focused.
For more tech-savvy people — like you, I suspect — I would recommend the far more cost-effective Backblaze B2. They offer a service similar to Amazon S3, but at lower prices and run by a less abominable company than Amazon. With one of the apps among their integrations you should be able to set up a syncing or backup solution that is cost-effective, low-maintenance, and end-to-end encrypted. I have used Backblaze for backups and large-file hosting for two years and they have proven to be good internet citizens who practise impeccable ethics and whose professionalism shows in the technical details.