Unable to Use an Attribute for Filtering

If you are trying to configure conditions for your feed but an attribute by which the filtering should be done is not available in the list of attributes at the Conditions tab, make sure that the attribute in question is enabled for filtering. Go to Attribute Settings in the admin panel and set the "Use for Promo Rule Conditions" option to "Yes". Refer to the screenshot below:

Save the changes, and after that you will be able to use the specified attribute to setup conditions in the feed settings.