that’s nasty¡!
mold around base of tree is not a great sign
does it drain (the pot?)
if not, you need to remedy this immediately <-do much homework on this first (so many threads here...YouTube also)....first first tho, gently tilt it on its side allowing any pooled water to escape
If no drain, what’s the pot made of -could possibly drill it?....now is typically not the best time of year for repotting is why I ask.
could be stanky fertilizer (hopefully)
if it’s what j is saying, you must stop watering until it needs water again...dry soil down to ~first knuckle. If pot is not draining, ignore this, fix pot problem ASAP
stagnant pooling water, rotting wet roots, and even some fertilizers can be fuuunky
where did you get it?
please address all questions if able to get at problem... also, a clear pic of the soil may help. please put in your location info.
winter is on the way, I wouldn’t put off addressing these issue(s)
Welcome!