formula for choosing between Mode and Median

Hello welcome to the forum.

One option would be to use the CHOOSE function, for example:

Formula:

=CHOOSE(MATCH(Validtion_Cell,{"MODE","MEDIAN"},0),MODE(Values),MEDIAN(Values))

'Value' is the range of numbers, and 'Validation_Cell' the drop down selection. Here 'MODE' and 'MEDIAN' are hard coded (MATCH) but could be read from sheet cells along with the drop down list.

Hope this helps.
DBY