The modern interpretations have included Orkney, Shetland, Northern Scotland, the island of Saaremaa (Ösel) in Estonia, and the Norwegian island of Smøla.

By the Late Middle Ages and the early modern period, the Greco-Roman Thule was often identified with the real Iceland or Greenland. Sometimes Ultima Thule was a Latin name for Greenland, when Thule was used for Iceland. By the late 19th century, however, Thule was frequently identified with Norway.[6][7]

https://en.m.wikipedia.org/wiki/Thule

But yeah they were aware of things beyond the limits of their maps. So idk id this is more accurately "roughly around the limits of roman maps" instead of "the area the Roman empire ruled".

Tacitus for instance talks about the Fenni and the romans definitely visited and knew the Baltic Sea, but there probably wasn't a whole lot going on around 100AD that would've been of that much interest to the romans. Fishing and relatively poor trading (by Roman standards).