Is it permissible for a woman to post religious topics (verses, hadiths, sayings of the predecessors) on social media pages where men are present, without speaking to them or exceeding the Sharia-compliant boundaries, and is this considered intermixing (ikhtilat) or a type of jihad for a woman, with the intention of gaining reward and recompense?

There is no harm for a woman in spreading religious knowledge on social media platforms, and this is not part of the forbidden mixing. Spreading religious knowledge is a type of jihad, as it is a jihad through proof and clear explanation, and it is the superior of the two jihads. A Muslim is in the path of Allah as long as he is seeking knowledge until he returns.