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If the vent is facing directly toward your neighbor’s garden, it can often be angled or redirected to disperse the air in a less intrusive direction. This is usually a straightforward adjustment that a ventilation or HVAC specialist/plumber.
Also work looking at upgrading the vent’s filter system. Standard kitchen vents often come with grease filters, but you can ask for one with additional charcoal or odor filters, to absorb the smell but you do not to change the filters typically every 6 months. This may require a slight modification to the vent unit itself, which is something an appliance repair or ventilation company could do.
I agree it’s something that isn’t ideal for neighbours.