What forumula does Excel 2016 use to extend data series?

I have a series of GDP data from various countries from 1990 to 2023. I need to extend the series to 2050 by dragging the lower right-hand corner of the selected series to 2050.
Can anyone tell me what formula Excel 2016 uses to calculate (forecast) the series?
Also, is there a way to change the way that the series are extended (forecasted) by, for example, using ARMA or ARIMA formulas?
Thank you in advance for your help.

Have a look at the FORECAST function: https://www.excel-easy.com/examples/forecast-trend.html