To enabled Advanced Lookup, log into to Power Platform Admin Center, navigate to
Environment >> [Select Environment] >> Settings >> Behavior
Enable the Lookup behavior and Save.
This adds the Advanced Lookup option in the Lookup dialog.
Clicking on it opens the Advanced Lookup Grid
We can perform SEARCH within a selected View, CHANGE a view, can FILTER it the results further to show only records owned, ADD a new record, SORT the grid.
The best part is we can open/edit an existing record as well as add new ones without losing the existing context.
Opening an existing record from the result opens the record in the new pop-up window as shown below.
Similarly, the Add new option opens the Quick Create form.
In case of special data type like Party List or Regarding, we can select multiple records of different entities we are presented with.
Similar the option to Add new records list all the tables/entities applicable to that lookup.
Thus the new advanced lookup makes working with Lookup much simpler and effective and we should start adapting / using it.
Hope it helps..