Flutter retrieve possible field values

I have a Flutter custom drop down field with several values. I want to retrieve a list of all the possible values in this field and print it on the page.

OR

I want to get a list of each field value used in a post without duplicates.

EXAMPLE:

custom field: beer_type
possible values: lager, ale, stout, ipa

Let’s say I have 3 posts and 2 are labeled as “lager” and 1 is labeled as “stout”. The PHP statement should echo:

lager
stout

Any help would be appreciated.

Thanks,
Jeff