If you refer to manual, it says on one of its first screen shots that this frequency is
Readout shows trigger signal frequency
Previous (first totally wrong and second somewhat wrong) guesses:
Educated guess - it is range of FFT display from 0 (left) to ~15 segments * 6.25 kHz = 93.75 kHz (right). Rotating the respective knob you must be able to change the scale.
Ok, I was proven to be wrong, and looking to manual I see no direct clarification how to interpret the data.
Here's my second guess: yellow
f= is not related to FFT at all, it is average, median, or whatever frequency measured by the scope using its yellow waveform. That's why
f= is yellow color, not pink. How noisy signal frequency is being measured may be a big secret up to scope developers :)
Do not ask me how scope measures it; may be it takes some "prevalent" frequency of noisy signal, or it uses some AI to guess what you want displayed frequency to be... As a test - use scope's calibration output (usually of 1 kHz) and this yellow
f= will show exactly 1 KHz.