Is there an API for spreadsheets?

Features like custom columns types, let’s say cutom custom country flags, or buttons would be a reason for me to switch to this platform compared to some other exsiting ones.
Cascading drop down is also mandatory.

The Button data type is currently on our roadmap.

A dropdown (Select or Multiselect) with Country flags can be created by using flag emojis icons today. We are also imminently releasing the ability to define Select and Multiselect options from a range or named range, allowing easy re-use of values in dropdowns from any range in any worksheet within a workbook (similar to how traditional spreadsheets allow data validation).

Regarding cascading drop-downs, do you have an example you can point us to? Curious to learn more about what you have in mind.

@Martin_Radley - REST API →