Hello! So, I think when Temmie Change compiled Escaped Chasm, she hit a box that removed all unused files from the compiled game. As a result, a lot of core RPG Maker files that she just doesn't use aren't included in the game.
For iconset.png, you can circumvent the problem by just putting a blank .png file with the missing file name in the img/system file of the project. So in my hack, I did it like this: https://ibb.co/p4yzd5r
It may say that it can't find any other files as well. Just continue to put blank files wherever it says that something is missing. If you want, you can even download my hack, Captured Canyon, and just steal the blank files I used and put them into your hack if that helps.
Hope this is useful, and good luck with your project!