VeraCrypt

I've been using this for many years to secure my personal data in a number of Veracrypt volumes. I keep them in OneDrive and also backup to another cloud service monthly. I decrypt each drive as I need to use it. It's essential to my way of working.

On Linux it does not work! It claims my (account) password (which it needs to mount an image) has illegal characters. Well, it works to log me in... And it then even shows these characters (my password) on screen. Showing the password on screen is a no-go. This showing (and also checking a password, which is kinda patronizing) should be a red flag to anyone. Unless I severely weaken my password, I cannot use this rubbish.

Been using VeraCrypt for over 4 years to encrypt my drives. Works perfectly both on Windows and Linux, and it's super fast and secure.

Easy, Secure and strong encryption. I use it for years by now

VeraCrypt is the gold standard of private encryption.

It is a free, open-source disk encryption tool that has been third-party audited. You can't get much better than that. With closed-source software, you can trust the name. The bigger the name, the more they want to avoid damage to reputation. With non-audited open-source software, you have to place blind trust often when dealing with complicated encryption.

Although its for disk encryption, you can think of it like file encryption. You don't need different encryption software to "lock" folders. You could also just archive folders and encrypt with something like 7Zip.

For the cloud, there is some limitations, especially with large containers. The big cloud services like Dropbox can already update individual files rather than the entire disk, but some less well known ones can't. For that, you might consider cryptomator. But it's not completely audited by a well-known third party. Though most of the cryptographic libraries it uses have been.

But you don't need to worry about anything other than things like IP logging and metadata with Dropbox or other commercial brands. Because you are using this as client-side encryption, those services can never see the contents. Even the government can't see the contents if you have a good password.