usage - How wide is singular "they" being used?

One might want to use a generic pronoun, that doesn't specify the gender of the person. Although "he" can be used in such case, they decide that "he" still reflect the history time when male was dominant. After searching in the internet, they find the singular they.

The problem is, what they learnt in school is they only use for a group of people. Someone may not know the existence of the singular "they", so it can lead to misunderstanding. Especially when after the singular they, the verb doesn't change to reflect the singular form:

When I tell someone a joke they laughts laugh.

So they want to know how popular the singular they get known in modern English. Is it safe to use it without any note?

_{Ok, I am them}