Excel 365 for Windows and now Excel 365 for Mac and Mobile apps have a great improvement to its drop-down list selector. At long last we have AutoComplete or Search for pull-down lists and you don’t have to do anything to make this work.
You can type a search into the drop-down list so Excel can show all the matching results. For example, type CO to reduce a long list of companies to one with only those two letters.

Search pull-down list
The search matches text anywhere in the string but ignores any blank items.
It’s simple to use, in fact there’s no visible change to the drop-down list at all. Here’s Microsoft’s demo
How to get searchable Excel drop-down menus
Absolutely nothing extra is needed. This feature has been added to all drop-down Excel lists automatically.
Who gets it?
AutoComplete for dropdown lists was originally just in Excel 365 for Windows.
It’s now in Excel 365 for Mac plus Excel Mobile for Apple iPhone, iPad and Android.