Not sure if there is reason for this, but some table fields do not appear in the select list when setting up a filter on a dashboard.
It seems I need to specifically set the data type to either be a ‘category’ or a foreign key. For example. I have column named ‘email’ which contains email address. In the data model, I set the data type to “email”, because that’s what it is and I like Metabase to auto format it as an email address. However, now that column is no longer selectable as a filter for dashboards.
The solution to this would be change the field type of the table in Metabase admin.
To do this, you can go to Metabase Admin > Data Models > Select your table > edit the type of the field to Category. You will be able to see it in filters now.