Search Writing|SE for the word 'ethnicity' and it returns over 100 entries. Many are questions that actually have the word 'ethnicity' in the title.
Virtually every week we see another question concerned about writing from the POV of another ethnicity, or questions asking how to describe people from different ethnic backgrounds. Recent examples which do not use the word 'ethnic or ethnicity' (so they would not show up in a search) include:
'Ethnicity' is the umbrella term, but some people like to debate what words mean, which is why I've added 2 links to Dictionary.com and wikipedia.
Wikipedia gives a broader definition than I expected:
An ethnic group or an ethnicity is a category of people who identify with each other based on similarities such as common ancestry, language, history, society, culture or nation.1 Ethnicity is usually an inherited status based on the society in which one lives. Membership of an ethnic group tends to be defined by a shared cultural heritage, ancestry, origin myth, history, homeland, language or dialect, symbolic systems such as religion, mythology and ritual, cuisine, dressing style, art or physical appearance.
This broader definition includes language, heritage, religion, and physical appearance, which probably covers many more questions that don't actually use 'ethnic' or ethnicity'.
Should we have an 'ethnicity' tag?
And to avoid the dictionary debate should the tag be 'ethnicity-religion-race'
Many of these questions resolve to the same answer, or very similar answers despite specifics in the ethnic group mentioned in the question – hence the reason for a common tag (not to put people in boxes, but to tag similar topics so the information is easier to find).