I'm using filen.io. E2ee and zero knowledge service from Germany. Their desktop client just works.

Nextcloud works well, and has a desktop client that integrates well with linux DEs (at least gnome and KDE).

Self-hosting is obviously what a lot of people do, me included, but it is not the only option. Nextcloud accounts are available through several hosting providers.

More info on the nextcloud website.

How much storage do you need and how much are you willing to spend?

I've been using pcloud. You can choose for the data to be hosted in EU. Doesn't have a client but works well with rclone (and Round Sync on Android). And from time to time they offer "lifetime" package - no subscription

I use sycthing and it'setup and forget.

I think of cloud storage as meaning automatic synchronization to a phone app and crap like that. If you just want plain storage, I'm happy with Hetzner Storage Box. The one I have is in EU so that adds some network latency. I don't think they have it in the US yet.

You could also go on lowenspirit.com and look at storage offers. servarica.ca has some nice ones that are supposed to be good, but I haven't tried them myself. They are in the Montreal area.

Linux only, SSH works fine. Not e2ee. Nextcloud works fine but extra work unless you use a service provider. It can be e2ee but not normally so. Syncthing worth a look too. It is not cloud storage, but direct device transfer. Bitwarden send is useful too if you want to juat send file someone, and thunderbird is working on thunderbird send which might be interesting.

Maybe Synology if you want your own lan NAS?

Jottacloud is pretty good. They have a Linux CLI too

Take pCloud - I paid one time, for a lifetime of 2 TB...

For me personally, I split up my data into different cloud storage solutions depending on the sensitivity of the data, and frequency of access on the data.

For stuff I need quick access to, I use cryptomator with MEGA. MEGA has a pretty decent Linux App, but recommend using with cryptomancer or any sync-friendly encryption tool so that they can't read the data.

For stuff I infrequently access, I personally just use Proton Drive. Plan to fully switch to using them once they have a functional Linux desktop application that supports syncing.

For more sensitive stuff like SSH Keys or documents that might contain my sensitive personal information, I personally just use VeraCrypt and store the encrypted file on a thumb drive, backing it up to another thumb drive every week.

Koofr has desktop client for Linux.

I've been using mega. They have a decent linux client and file manager integrations.