Above a certain zoom level (around 5e+12 depending on the screen size) the app enters the deep zoom mode and starts using custom floating point numbers which significantly slows the computation.
The paint modes and the interior painting are not supported in the deep zoom mode. The app automatically switches to the Classic paint mode for the exterior and None for the interior.
The higher the zoom is the longer numbers are necessary (up to 1024 bits long) and the slower the computation is. Zoom is limited to 1e+300 but when you exceed 1e+100 the computation can take some time and you may need patience to get a fully rendered image. Fortunately there are lots of interesting spots at much lower zooms.
The deep zoom mode is not supported for all the fractal types (at the moment it is supported for 25 of 40 fractal types).
You are welcome to ask your questions in the comments.