The R word is "Retard".
Folx is supposed to mean "Folks" but in a more inclusive manner because it also includes non-binary people etc.
Now you might want to say "Folks" is already all-inclusive and you'd be right to make that point, but the idea is that by Folx, you are going out of your way to signalboost you don't just mean everyone (men and women) but everyone (men, women and non-binary).
Your last point is actually a good point that i haven't thought about much before, i'm extremely online and up2date with internet slang and the likes and even i get sometimes confused when reading some woke 19 year olds tweets.