Quote:If you’re working with others on a shared Google Sheets file, sometimes people can enter unexpected data or something that breaks a formula. One way to ensure everyone enters the data you want is to provide it for them in a drop-down validation list.

How to Create a Drop-Down List

A drop-down list is a great way to ensure the data people enter into your form, application, or spreadsheet is exactly what you’re expecting. It also provides a much faster way for people to input that data since they’re selecting from a pre-configured list you provide.

The first thing you need to do is open up your Google Sheets file and select the cell(s) for which you want to use a drop-down list.
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Full reading: https://www.howtogeek.com/395616/how-to-create-a-drop-down-list-in-google-sheets/