3rd level key has no effect, how do I make it work or are there any other good ways to type less common characters quickly?

I installed the gnome tweak tool, and went to "Additional layout options". There are several possible keys that can be assigned to choose 3rd level, I tried right Alt and right Ctrl and both of these seem to have no effect at all, that is, they don't change which characters are typed. (I tried to press them at the same time with a key, and also tried to press them before a key, both results in no modification; I also tried 2 text editors, the built in one and Sublime Text, and there's no difference too).

"Compose" key seems to work but this method is too slow and hard to remember and I don't like it.

So how do I fix the 3rd level functionality?

The input source I'm currently using is "English (US)".

Solution 1:

The standard "English (US)" layout doesn't have any characters associated to the 3rd level key, so it's not surprising that the key does nothing.

Add "English (US, international with dead keys)" or something similar to your input sources and use it to access some extra characters.