VELYKI DMYTROVYCHI, Ukraine—Anna Datskiv is turning her back on Russia as she makes her kutia, a traditional Ukrainian Christmas dish of sweetened grains, a couple of weeks early this year.

Like many other Ukrainians, she has switched to celebrating Christmas on Dec. 25, as in most of the Western world, rather than Jan. 7, as in Russia. It is part of a broader shift in Ukraine since the war began to move away from cultural traditions that reflect Russia’s centurieslong hegemony over its neighbor.