This is exactly the same as my MandelSplit app, but optimized for 64bit ARM including double precision NEON.

In short:
LONG PRESS to bring up the settings dialog.
TAP to prioritize calculation. (This comes in handy when you want to see a certain part of the image without waiting for the entire calculation to be finished. Try it. TAP again.)

No ads. No permissions. Free software.

Why are there 2 apps? So that you can install both and compare the speed difference. By doing so you will learn part of the advantage of your 64bit phone compared to a 32bit model. There are other advantages of 64bit devices, but this app only shows you the speed gain. It is a kind of benchmark that shows you how fast your device can be if properly programmed.

Performance gain on my device (yours could be different): at lowest precision 2 times (NEON), at medium precision perhaps 1.5 times, at higher precision again 2 times (64bit)

When you want to measure by yourself: draw the same image in both apps and observe the value iter/sec, which tells you how many iterations your device can compute in one second for the given precision. Because the app does also other things beside calculating iterations (like drawing) the iter/sec value is lower when the image is simple and there is not much computing.