Most tropical cyclones rapidly weaken over land, however, given some conditions (such as very wet soil/ground cover and tropical lower atmospheric conditions) they can sustain themselves or even intensify over land, in a phenomenon known as the brown ocean effect. So, is it at all possible for extreme "brown ocean" conditions or other potential factors to result in not only the maintenance but the formation of a tropical cyclone over land, either from an extratropical system or not? The intensity and duration of time that the storm would last without transitioning to water is irrelevant—even a few hours at tropical storm levels would be a yes.
No, it isn't possible for cyclones, hurricanes and typhoons, which are all different names for the same thing, to form over land. Storms can form over land, but not hurricanes, which draw their power from the sun-warmed ocean and rapidly lose their strength when they hit land. The power of a typical hurricane is immense, probably in excess of 50 megatons, which was the yield of the largest hydrogen bomb ever tested (by Russia).
Yes, it would be possible for a tropical cyclone to form over "land" in extreme circumstances. Tropical Storm Claudette of 2021 is a notable example of the phenomena known as the "brown ocean effect". It formed over "land" areas of Southeastern Louisiana, which is a lot of marshy, swampy areas. The actual areas of land helped tighten the circulation enough for classification as a tropical storm (the disturbance was already producing gale force winds 12 hours or so prior to this point). The disturbance was already nearly a tropical cyclone before reaching Southeast Louisiana, with deep convection. However, the low pressure system was broadly organized, which the brown ocean effect tightened it up just enough. It is an interesting scenario and stuff like that is tricky to forecast.