The Clear Formats feature is the most common way to remove format from cells in Excel. Of course, it supports to remove all kinds of date formats.

Select the date cells that you will remove date formats from, and click Home > Clear > Clear Formats. See screenshot:

Now you will see all kinds of date formats are removed, and dates are converted to 5-digit numbers in bulk. See screenshot:

Note: The Clear Formats feature will remove all cell formats, including number formats (percentage, currency, time, etc.), alignment formats (indent, wrap text, merge cell, etc.), font formats (bold, font color, font size, etc.), borders, fill color, etc.

If you need to remove date format only from cells, but remain the other cell formats such as font size, fill color, borders, etc., you can try this method.
Select the cells that you will remove date formats from, and click Home > Number Format > General. See screenshot:

Now only the date formats are removed from the selection, and other cell formats are remained.