There are few ways! From the help page: "To make a permanent join, either use the Join Field tool or use the joined layer as input to one of the following tools: Copy Features, Copy Rows, Export Features, or Export Table." See more: pro.arcgis.com/en/pro-app/latest/tool-reference/data-management/add-join.htm

If you have multiple rows that share the same fips (or whichever identifier) - then you need a different kind of join! Namely, a many to one join which is a different process. See here for more on the particulars of that in Arc: pro.arcgis.com/en/pro-app/latest/tool-reference/big-data-analytics/join-features.htm Please note that the process is particular to the data and other methods might be better.