How to make an relation attribute as autocomplete in advance search of Backoffice?

In our Data model, We have created new type(FeatureNBenefit) and then a new many to many relation of the newly created type with Product.

I am able to add FeatureNBenefit in advance-search of backoffice, also all applicable data for FeatureNBenefit is shown in dropdown in advance search.

I am able to select data from dropdown but when I try to write some text then no autosuggestion is coming in dropdown.

For supercategories autosuggestion is coming in advance search but not for my custom attributes.