Adobe Acrobat prepare form-Dropdown Options-Wont let me add more than 21 options?

I've had drop-downs with thousands of items, so no, there's not a limit of 21 items.

Please let us know what happens when you try those additional items. Also, are you doing it manually, or using a script? If the latter, please post the code you're using.

What happens when you add more than 21 options.?

You need to ask program questions in the forum for the program you are using
To ask in the forum for your program please start at https://community.adobe.com/
Moving from Using the Community (which is about the forums) to the correct forum