Hello,
you should find the answer here:
https://community.mendix.com/link/space/connectors/questions/92705
or here:
https://www.youtube.com/watch?v=-seyrOmIhNc
or here
https://medium.com/mendix/easily-create-custom-dependent-drop-downs-in-mendix-343a38b8041d
Dont use a enumeration for this.
The entity you be called shop, with an attribute Name.
The app admin should be able to manage the list of shops.
The idea entity should reference the shop entity. Each idea refers to one shop and on shop can be referenced by multiple ideas.
When adding an idea, a shop should be selected out of the created list by the admin
When selecting a shop, you can now show the referenced list of ideas.
If you need more guidance, check the rapid developer course of the mendix academy. Or i can teach you through our program.