looks like some mushroom feasting on your degrading bark mulch.. or something in your media ...

tease it out with a fork or spoon ... or leave it be and see how big it gets ..

i highly doubt it has anything to do with the ficus ..

i sterilize everything in the microwave before i use it indoors.. just to avoid this type of thing ... more for bugs and stuff.. but it also cuts down weed seed also ... or spore in this case ...

ken

https://tipnut.com/sterilize-soil/

Hi Ken,
This pot was actually outdoors last summer so definitely not sterile!

I don't mind it, just found it oddly cute! And very different than some I had growing in another pot with a mostly peat mix (don't have pics of that one).