What's wrong with encrypting individual files? It is easier and it also doesn't cause reading problems for your OS, and more importantly it doesn't decrease the lifespan of your disk because it is not as intensive and it doesn't have to happen every time you access the disk.
Because it's more complicated and I don't want to do that for each individual file.
All I want is to have password protected encrypted USB or one password protected (and maybe even hidden) folder on that USB drive, so I can put all small backup files there.
If you only use Linux, use LUKS since most distro support it. But if you use different OS and you wish to unlock the USB on multiple OS, i don't know what option is available for you.
I will check out LUKS, but I wanted to have something that works both in Linux and Windows OS because I use them both.
Tails was my first option for Linux OS, but I was also checking out Qubes OS.