Hello there
Please take my advice with a grain of salt because I am really new to bonsai but your leaves look exactly like the leaves on my trident maples and I was given great advice on here, it’s a fungus not really sure what type but I went to a Home Depot and purchase some Daconil ready to use spray. Make sure to read the instruction and shake the bottle first, mine had so many leaves infected that I had to remove about 60% of the leaves before I sprayed mine and so far it’s been working great and they are getting new leaves. But like I said mine is a trident maple and I am by no means any type of expert, I attached some picture of what mine looked like to compare with yours, I hope it helps a little. Just wait a little bit the people on here are wonderful and are so knowledgeable I’m sure you will get some really great advice and good luck ?