You can restrict the linked records options by adding a "conditional filter" to your field. When a filter is selected on the form, it will limit the linked records available in the list. The conditional filters for the form can only use the linked records field and lookup fields. To elaborate on this functionality, you can watch this video.
On the legacy site app.miniExtensions.com
Click on the linked records field that you'd like to add filters to.
Go to the option under the Filtering & Sorting Records section:
Nested linked fields are not supported. Learn more about this function's limits here.