There are two questions here. I hope at least the second one is not off-topic for Stack Overflow.
The second question is very short:
The first question is longer.
Could anybody explain why CSS 2.2, compared to 2.1, feels like a "second-class citizen"? For example,
the Wikipedia article about CSS mentions CSS 2.1 fifteen times, whereas CSS 2.2 only once
https://css-validator.org/ and https://jigsaw.w3.org/css-validator/ provides an option to validate 2.1, but not 2.2
According to this: https://github.com/w3c/csswg-drafts/issues/2008 discussion, CSS 2.2 is merely 2.1 with incorporated errata, but this doesn't answer why 2.2 didn't gain any traceable, on the Web, mentions.
To make it easy, the two versions are CSS2 and CSS2.x where the "x" doesn't really matter. The working group made big changes to the CSS2 spec to create a new one (the CSS2.1) then later they did more correction to have the CSS2.2.
Basically, CSS2.1 and CSS2.2 are (almost) the same compared to CSS2.
CSS 2.2 is the second revision of CSS level 2 [CSS2]. It corrects a few errors in CSS 2.1, the first revision of CSS level 2. ref