How do I change my pivot chart X-axis to show my date formats that are "DD/MM/YY HH:MM:SS"

Can you upload a sample file that illustrates the problem? Maybe include a few links to those articles you have already tried.

Finding a random data set on the forum and creating a pivot table and chart from it, I found the opposite problem. The data would be shown as dates, and Excel would not let me format the pivot chart's x axis to show the dates as serial numbers. In order to recreate the problem you describe, I needed to delete the date formats from the source data and the pivot table before creating the pivot chart. My various quick tests suggest that, once a pivot chart gets the text for the horizontal axis labels/categories, it does not want to change them.

I know that pivot charts have a few severe limitations. Pivot charts cannot be scatter charts or use a "date" axis, for example. I wonder if something in this limitation where pivot charts want to only work with text on the horizontal axis prevents you from changing number formats.

I don't know if you have tried this. Considering that pivot charts are limited to "text" only on the horizontal axis, I wonder if this is a case where you will be better off creating a regular chart to regain the ability to use numbers on the horizontal axis. Creating regular charts from pivot data is tricky, but not difficult. See tutorial here: https://peltiertech.com/regular-char...-pivot-tables/