Hoe to get the number of data points on X axis

I am currently plotting a box plot along with the data points on top of it. This chart works fine. I am wondering if there is a way to add to the X-axis the number of points that box plot uses for plotting. Like say my X-axis has “A”, “B”, “C” etc and say the box plot plot of A had 60 points and B had 20 points and C has 80 points that my X axis should have “A [60]”, “B [20]” and “C [80]” instead of “A”, “B”, and “C”.

I tried changing my x in my data frame to include the numbers but the whole processing turns out to be very slow for larger data frames (1M+ rows).

Any help is highly appreciated.