I have an indoor ivy plant and it has a layer of spiderweb/fungi looking stuff on the very top. What can I do to fix this or how to treat it?
If this is a white mould growing on the surface of the substrate of your indoor ivy and it is not moving about lol (if it moves it is an animal of course), then it will be some quite innocuous fungi which are now seen as a sign of a healthy, well balanced substrate and an indication that the Rhizosphere (the ecology of the substrate and organisms) is thriving.
You really have nothing to worry about unless it becomes smelly, wherein your problem is not the fungi but an indication that someone has been overwatering the plant.
Ivy is a epiphytic plant that is a climbing plant despite people routinely expecting it to thrive by dangling down over the pot edges, so, if you want it to prosper, provide it with a simple wooden trellis, a moss pole or an untreated wooden plank and it will bed into those supports and will grow much faster.
It is not often appreciate how much roots depend upon oxygen and a well draining substrate is vital, however, roots also develop a symbiotic relationship with the microbes in the substrate, seeping out sucrose and other photosynthesis derived sugar products into the substrate to feed the microbes and in return they break down organic materials faster in return.
Anything you do to disrupt that balance will have a negative effect on the root system and therefore the shoot system above the substrate, so please avoid putting so-called home remedies on and in your substrate which include cinnamon and hydrogen peroxide. Provided you have a well draining substrate appropriate for the plant, you learn how to test when and how to water the pot/substrate and never over-water, you need do nothing more to your plant except for the occasional fertiliser and for uniformity, a commercial brand of granules dissolved in water to the right concentration is preferred since you know what it is you are adding to the mix. Again, avoid the countless "grandma's special recipe" nonsense which, often when analysed provides little or no nutrient value to the substrate.