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.

I've seen people recommend https://filen.io/. I've created an account but I haven't actually used it yet. No red flags so far.

If you want to put in some work i can highly recommend self hosting a nextcloud/owncloud, maybe together with some family members.

Something more obscure you can do is create a shareable public link with or without password to share large files with whoever you want.

On the downside, whenever i see a professional use we transfer or the like i cringe massively.

lmao, ToS never works. Libre software does.

They say it's secure but I don't trust them. You can find several alternatives with much better privacy like Koofr (vaults are zero knowledge) and protondrive. Both are European 🙂

You can also use any service and encrypt all your data using dedicated tools for backup like Borg or specialised tools like Cryfs and synchronize your local files with Rclone 👌

Depends on your security and feature requirements. I found that Mega works well for music streaming on mobile, and the E2EE is reasonably trustworthy for that use case.