Whats is happening to my indoor begonia? Insect or fungus see pics
I saw one tiny white speck moving around on the soil. Could that be whats eating the plants?
Certified GKH Gardening Expert
This, actually, looks more like a fungal issue, possibly shothole fungus.
The best way to deal with this is prevention, such as letting the soil dry out almost completely between waterings, and keeping the plant trimmed to allow for airflow between it.
For now, a mix of 1/4 peroxide to 3/4 water will help.
This article will give you more information on the care of these: https://www.gardeningknowhow.com/ornamental/flowers/begonia/begonias.htm