A store Feature is not visible as an optional check-box filter when searching for stores on the Store Locator.
In order for a Feature to display on the Store Locator as a filter, it must be "highlighted" in the Brickwork CMS. This can be done by going to the ⚙ icon and selecting "Global Content", then scrolling down to "Features", and finally selecting "Highlight this feature?". You can confirm that a feature has been highlighted when the text then changes to "Unhighlight this feature?" instead.
More information about creating and updating store features can be found here.