LOOKUP FIELDS AND FILTERING
Another very useful field type in SharePoint business forms is Lookup field. The possible values are populated from another SharePoint list, instead of term store or static choice values. This allows you to do some interesting things such as having a one list for orders and another list for order rows, and when you are editing an order row, you could select a product from products list, and so forth.
In the example above, I use value of Car class field to filter Car type field choices with relatively simply PowerApps formula. Both Car classes and Car types are separate SharePoint lists on the same site.