Upgraded from 1.39 to 1.42 using the link posted above.
I agree, the FFT function would be much better if it supported cursor movement, and showed Amplitude and Frequency in a rectangular box as the cursors are moved, with the ability to toggle LOG mode for Y-Axis.
It's not bad... it's quite promising actually, but without at least the frequency displayed (when moving the horizontal cursor), it's not currently what I hope it could become.
See the image attached here. It appears that in 1.42, the discontinuous trace problem is back (circled in blue).

Back to the FFT, there's a good bit of code that goes into the fast fourier approximation to the z-transform and this depiction of the approximation to the magnitude of the power spectrum.
You'd really want that code space dedicated to existing oscope functionality first, then FFT being icing on the cake.
I am not complaining since these releases seem to be getting better and better, the device more valuable. I do not view this as a toy, but rather a tool, and ZOTI seems to be making it better and better with subsequent releases. YMMV.