However, the Rema says that people in Poland/Ashkenaz were decidedly lenient on this matter. They’d drink non-alcoholic beer among goyim, and if we thus accept the Rema, then social activities involving drinks (such as coffee, etc.) should be ok.
That is misleading. The Rema does not distinguish between alcoholic beverages and non-alcoholic beverages; he distinguishes between date beer and everything else.
According to the Rema, everything that is kosher is okay, except for date beer.
If someone were to claim l’halacha that a bar is assur, but hide the fact that according to the same reasoning Starbucks is assur, they would be arguing disingenuously, since they know full well that it is likely their audience would not accept their argument knowing it pertains to coffee shops as well.