I’ve seen older posts from 2010 saying that adding this was on the todo list for the devs, I was wondering if it was added yet, and if so how do I do it?
See Data > Statistics > Fourier Analysis as of LibreOffice 6.3.
Thanks to Lupp for the link to bug 74664, it is mentioned there.
There still is enhancement request tdf#74664 of 2014-02-07. It doesn’t explicitly address FFT, but Fourier transformation in general. I do not know the solutions the other mentioned software has implemented…
As @Lupp said, it’s not possible with Calc, so you need to try other software. Two really good F(L)OSS packages for scientific data analysis are SciDAVis and LabPlot.
LibreOffice version 7.0.5.2 (which I am currently using) has a FOURIER function that you can use to run both forward and inverse transforms.
Additionally, this same functionality can be accessed through the menu Data->Statistics->Fourier Analysis…
Have fun with your transforms!