I use pCloud
https://www.pcloud.com/. It's designed for cloud backup and file synchronization. It offers a desktop app for Linux, Windows, and Mac, and it also has Android and iOS apps (see more info about that here
https://www.pcloud.com/features/accessibility.html).
If you prefer, you can simply access it via the web browser instead, which is what I do.
A basic plan is free (this is what I use - I only use it to shuttle files back and forth between my phone and computer), but if you're needing to store more than 10G then you would need to get a paid plan. The plan pricing seems quite reasonable for the amount of storage you get.
I can't comment on how good the Linux desktop app is, because I always access it through my browser instead. I don't use pCloud for proper file syncing or for long term storage like you're seeking to do, although it's certainly designed for those things. It's definitely worth looking into.