This is what I found in the MT McGinley Dynamic source code:

   mcg[i]   = ma[i+1]+(price-ma[i+1])/(McgConstant*McgPeriod*MathPow(price/ma[i+1],4));

Where ma = the moving average over selected price (default Close)
mcg = the computed output
The indices are in reverse order: higher indices go back in time.

Note that the MT version is not McGinley at all, not even McGinley computed over a moving average, because the term mcg[i+1] is missing on the right side.

The description of the MetaTrader version https://stonehillforex.com/2022/01/mcginley-dynamic-indicator-as-a-baseline-indicator/

The metatrader version of the McGinley Dynamic indicator includes a moving average of selectable type and a "constant" parameter that seems to blend the actual McGinley with the moving average (SMA, EMA,Weighted, etc)

Does anyone have an idea what the MetaTrader version is doing so I can reproduce it exactly on cTrader?

Thanks for the update, but I just saw an SSL indicator has already been published. So I think I just remove mine.