‎احسن الله إليكم Shaykhana, I’ve heard when it’s raining the Jamaa salah in the masjid is excused. Is this correct? If so how heavy or light is the rain is in this scenario? ‎جزاكم الله خيرا وبارك الله فيكم

Yes, rain is an excuse, and the measure is hardship. If it is continuous and not light, wetting the clothes and making the way difficult, or the ground around the masjid is mud and slippery, you are excused, and if the rain is light or has stopped and the road is easy then there is no excuse.