The device directly on the border is likely to cause problems with the TA noise. The direct intake area must remain under its own control to ensure the flow-related required conditions. So twice no :P.
That's why the ideal solution would be an air heat pump where the intake and the blower are stacked instead of the "corner" version. Is there such a thing? Does anyone have experience with it?
No matter whether allowed or not, the neighbor can probably build or place something there at any time. Whether hedge/bush or a wall made of firewood or carport or noise barrier (and then for good reason) or car, or trailer or bike trailer with structure or ...