Modern List Lookup Columns
Lookup columns, will allow you to connect a list to a column from another list you have on your site. Once connected, you can easily “lookup” other information and include this in your new list. This makes it easy to maintain team-level, centralized lists that contain information you use repeatedly.
Once rolled out to your tenant, you will see "look up" column as an option in column creation for lists and document librarys.
The Targeted release (entire org): will begin rolling out in late November and expect to complete rollout mid-December.
Standard release: will begin rolling out in late December and expect to complete the rollout by late January 2021.