You can allow your users to add an option to single or multi-select fields. To enable this go to:
Form Fields
Click on the single or multi-select field
Advanced section
Turn on Allow users to add new options toggle
💡Note
When you are using dropdown for the selection field, you have to type in the new option and the option to add it will appear
If you're using multi-page forms your users may experience "invalid selection" errors when adding new options and advancing to the next page. This is due to how this feature works behind the scenes to avoid Airtable's limitations. There are two ways to avoid these errors:
Have the fields your users are adding new options to on the last page of your form.
Use Save & Continue mode.