Wouldn’t a church celebrating the mentioned “harvest festival” be rather, well, pagan?
I respect a person thinking through the issue and following their own conscience.
As for the harvest festivals, I have no opinion on that. When I was growing up my church would throw a big halloween party. It was fun, but not because it was a halloween party, just a party. But conscience clicked in years later and they started having harvest festivals.
The only think I really like about halloween is the candy. I can have that anytime. So I can live without it.