Will it be illegal to sell anti-drone systems to any nation like Gaza? Because it's not a weapon system, it's more like a defensive technology. Would it still violate an arms embargo?
In the US, it is illegal to sell screwdrivers to Gaza without a license, see 31 CFR 595.409. There are numerous rules pertaining to the Palestinian Authority staring here. Dept. of State has a partial list of countries and their associated restrictions, if you want "like Gaza", and note that they warn you that this is not a complete list. If you are specifically interested in weapons-related restrictions, the US Munitions List is here. There is no generic "anti-drone" system, so you would have to look at the specifics of a system to see if it is on the restricted list, or not.