From my side there is a few options to use. But what I would do is create a dropdown menu entity with a association to your main entity. Create the objects in the dropdown entity and then you will be able to multiselect the object using a reference set selector or any other way you choose.
If you do not want to take that approach, you can just add the countries as attributes in your entity with Booleans. Then you can give them check boxses on the page.
An enumeration is 1 attribute that can have only 1 value at a time, just like a ‘Name’-attribute can only contain one text. So in case you want to select multiple options you have add that to your domain model with a market entity and a *-* association from ‘service information’.
Remember the Market entity needs data so you have add the markets by hand or microflow (only once)
For the UI you need a reference set widget from the marketplace like https://marketplace.mendix.com/link/component/2349. or https://marketplace.mendix.com/link/component/116917
thanks for the quick reply.
I have downloaded the simple checkbox selector and added some markets manually to the markets entity, but sill only have the option to choose one attribute at a time. I created the many-many association between my data view “service info” and “markets” as well.