How do I address a stuck or dead pixel on my MacBook screen?

Refer to About LCD display pixel anomalies for Apple products released in 2010 and later - Apple Support.

Apple's decision to replace the display under warranty is predicated on the number, location and relative proximity of the affected pixels. For example the presence of several affected pixels in close proximity to one another is likely to be a covered defect. A fewer number near the middle of the display would also be considered sufficiently objectionable. A couple near the perimeter of the display is not likely to be considered a covered defect.

Apple's determination is based on defined criteria which can be somewhat subjective, but their judgement is final.

From your photograph it looks like "foreign material" which could be an insect, not that it matters.

Even though you provided a surprisingly clear & HiRes picture, I cannot tell for sure.

You will have to have Apple or an Apple Authorized Service Provider examine the display to confirm if it will be covered by warranty. Apple always has the final say on coverage. If Apple declines coverage, then politely ask why and to explain that blemish. If you would plan to contest a denial of coverage, then I would want Apple to provide a written note on the inspection sheet clearly stating the blemish so you can receive a copy of the report to discuss with higher ups with support or even Apple corporate.

Please keep us updated as I am interested in what Apple has to say about it.