Ficus Ginseng drops leaves?

Hi guys, i have a problem with my ficus ginseng, everyday it drops 1 or 2 leaves in the pot, i don't know what's the problem, is it over-watering or is it root rot or not getting enough light? please take a look at the photos and tell me what u think from the look of leaves and trunk and what to do to save it, is this brown trunk at the bottom root rot or just wet from watering, although i water it every week or so, and what's the amount of water that i should pour on it, thanks in advance.

Update:

I searched a lot and it's so confusing for me coz most problems has the same symptoms, so i dont know which is which, i hope someone gives me a more specific cause.

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