Join syntax not being recognized by SSMS

When I try to build a simple join query, all of the join syntax is not being recognized by the query editor (inner, outer, left, right join).

FULL and ON are still recognized. I have never seen this happen and there is nothing on the internet about basic syntax not being recognized in this SQL Server version. What am I missing?

That's a feature called IntelliSense, telling you your syntax isn't correct (yet). You can turn it off if it bothers you, but the whole point of the feature is to highlight your syntax when it is incorrect or incomplete.