I’m exploring this now too 😂 Found several search results. Here’s one explanation I found:

“The best way to understand fernweh is through analyzing exactly what it is not—homesickness. A familiar term and common feeling many have experienced at some point in time, homesickness is an acute longing for one’s home during a prolonged time in its absence. While homesickness can lead to distress and suffering, it is nonetheless, in most cases, a mendable ‘sickness’—we can always return home. Fernweh, or farsickness, is also a suffering, but is less clear cut and rectifiable. It is a consuming longing to be somewhere you’ve never been; an aching to be in a distant and unknown land, an ambiguous yearning for anything, anywhere else, as anyone else. But how do we go about searching for a place we’ve never been? How do we assuage a yearning, the source of which is unknown to us? And the most pertinent question remains: why do we ache for places we’ve never known?”