That is true, it will be to the Gregorian calendar. Some use that instead of recalculating each year. I do for many as I’ve way too many festivals to shift otherwise. Only one do I recalc each year as that is based on the lunar calendar as its a lunar festival.
As far as Wep Ronpet, I will agree, most will be different. Again some use the rising of Sirius in varying locations, some stick to the same date each year and others will no doubt do something different. I have two for example: Summer solstice which was one of the three markers in early dynastic (mainly because the other two don’t really apply to me such as the Nile and Sirius rising). And the other around the first week of August like some others (though I think it should actually properly be September) as my main festival calendar is based on dates which make that the start of the year.
Its fun. A good point to keep in mind is that they often messed with their calendar anyway so its fine if we don’t agree. Well, that’s what I keep telling myself