There are enough of international and European days and events which are none of those like the Earth day. Some relation to religions does not matter if its widely observed and mostly neutral but some of the days are completely focused on religious persons or events. Why not just have neutral celebrations like for the start of the summer or just Settlers related imaginary days
Also (semi) related to all of your A, B and C currently of the settlers special days in November is for Guy Fawkes and we get some gunpowder in the mail. It can seem kinda odd for a non UK people that we celebrate a terrorist or a terrorist act that failed. Maybe its just a fireworks fun fair today for people but the history of the whole thing is very grim