Fatwa of Sheikh Abū Bilāl ḥafidhahullāh (summarised).

There are four types of masjids in terms of giving lectures: 1⃣. Masjids of Ahlus-Sunnah. With these masjids, there is no issue whatsoever in attending, lecturing, admonishing and conducting classes therein. 2⃣. Masjids belonging to the common folks (’awām) who generally love khayr. Usually these type of masjids allow everyone to give talks as they are unable to distinguish between the different speakers. With regards to these types of masjids, we shouldn't leave it for the ḥizbiyyeen. Rather, we should visit them and advice the people therein in hope that they take more benefit from our lectures than those of the other groups; because we invite to good based on clear evidences, and maybe as a result, they invite us to come back more often. 3⃣. Masjids that are under the hizbi control, although they have lost interest in these masjids. In this case, it's okay for one to give occasional reminders on the go, but no official pre-planned lectures; as this is reserved for the masjids of Ahlus-Sunnah and because giving official lectures in these types of masjids will only revive the masjid in the favour of the hizbees. 4⃣. Masjids belonging to hizbees who are stubborn upon their bid'ah and Hizbiyyah. We should not visit these masjids at all; not for the occasional reminder, and certainly not for lectures. Source: https://t.me/madrasatuna/2516