I have a 2 year old Thaumatophyllum bipinnatifidum (my covid baby). She's been growing wonderfully all winter. See one pic of how glossy and green the leaves were. I haven't changed anything in terms of light or watering. Her lower leaves are all dying. And the upper ones have brown spots. Help! What is wrong?

Its natural for the lower leaves to die off. That is how this genus of plant makes a trunk, which is what distinguishes it from Philodendron and why it was given its own genus, Thaumatophyllum. I can't see the brown spots so I don't know what that may be