There are now three different lookup solutions available for use in Flow screen:
The ‘Official’ Lookup component
The ‘Official’ Lookup component, also known as the Out-of-the-box (OOTB) component, ships with Salesforce. It’s available in the standard components section:
The Official component works by referencing existing Lookup fields.
The Unofficial Aura Lookup Component
This powerful community component is available here.
It has many advanced features.
The New LWC Community Lookup Component
The community is converting the older unofficial Aura component to Lightning Web Components. One advantage of this is that it will allow the use of Custom Property Editors for a more usable configuration experience. This is currently available in code form here.