LINQ To Entities supports Contains method but only on scalar types.
LINQ To WAQS also supports it for entity types.
So, if you use a contains on an entity type collection, LINQ To WAQS uses the entity key to transform our entity collection to a scalar type collection if the entity key just contains one property. Otherwise, it uses an aggregation of AND and OR.
So, for example, you can use this query:
await _context.Products.AsAsyncQueryable().Where(p => SelectedSuppliers.Contains(p.Supplier)).ExecuteAsync()