Add an explicit wait after you click your menu and then once the drop-down element is present refer below steps:
https://selenium.dev/docs/site/en/support_packages/working_with_select_elements/
Please refer to the above document:
You can use the select class in ruby to achieve this:
select_element = driver.find_element(id: 'couCode')
select_object = Select(select_element)
To select using text:
select_object.select_by(:text, 'URUGUAY')
Using Value:
select_object.select_by(:value, 'UY')
Using index:
select_object.select_by(:index, 1)
Note:
instead of puts a.text + ', '. Try, puts a.attribute("textContent") +','