Whenever we have a scenario, wherein we would like to make use of Quick create form in one model driven app and not on the other so we ideally un check the option available for disabling the quick create form however the same action isnt supported as per the following below reason.

According to https://docs.microsoft.com/en-gb/powerapps/maker/model-driven-apps/create-edit-quick-create-forms, updating the 'Enable quick create form' setting on the entity will impact entity scope, other than model driven app scope so the feature wasnt supported yet, however users has complained of the feature and want if this can be considered as a feature improvement