I don’t want to write up a whole paper at the moment but I’ll note that you really shouldn’t be trusting any cloud providers with your data, because you should always be fully encrypting your data before they get their hands on it. Plasma Vaults (if you use KDE) are one way to do this, or you can use something like Cryptomator, gocryptfs, etc. Basically how it works is that you store files encrypted in one directory (/home/me/Encrypted), then transparently unencrypt that data to another mountpoint for your regular usage (/home/me/Unencrypted). Modifications in the Unencrypted directory will automatically affect the Encrypted directory through the use of magic. The cloud provider will only sync the Encrypted directory, and without the key they know nearly nothing about what your data is.

Given this sort of workflow, you can store your data anywhere, as long as you have a nice (open-source) way of syncing to that provider that can’t introduce any further vulnerability.