What is the ruling on sitting alone to perform post-prayer remembrances and the remembrance of Allah until sunrise in a mosque where innovations of audible and congregational remembrance are practiced?

There is no harm in sitting in a mosque where there is innovation (bid'ah); due to the Almighty's saying: "And no bearer of burdens will bear the burden of another." And Ibn Umar's departure from the mosque when he heard an innovation does not indicate the prohibition of remaining or the obligation to leave, but rather its permissibility. Scholars have mentioned the permissibility of leaving the mosque after the Adhan for an excuse, and such an instance indicates the permissibility of leaving, not its obligation.