Is listening to a lecture to be prioritized over performing the regular Sunnah prayer of Maghrib, especially if the lecture time is directly after the Maghrib prayer?

Prioritizing a supererogatory prayer over a lecture is more appropriate if there is a concern of its time expiring, and there is no contradiction in combining both.

As for preferring the pursuit of knowledge over the regular Sunnah prayers, it is not absolute but varies depending on individuals and circumstances. Ibn Taymiyyah said: "What is most virtuous varies according to people." Thus, writing Hadith might be more virtuous for some scholars, while two rak'ahs at night might be more virtuous for some shaykhs. It might also be most virtuous to combine both, or a less virtuous act might be better for a person than a more virtuous one. The preference can also differ for the same person depending on their situation.

Combining the pursuit of knowledge with performing supererogatory prayers is more appropriate and virtuous. Imam Al-Shafi'i used to divide his night between writing, praying, and sleeping. Similarly, most of the righteous predecessors combined seeking knowledge with performing supererogatory acts of worship.