It's not clear to me what you want to measure in this way.
You send to CH1 port CW frequency 4MHz. Lite sweep in span 500kHz.
Measure result - this CW frequency go to mixer and mix vs sweep signal. And output IF sweep in range 500kHz.
So on display you see internal digital filter around 60k (additional you see mirror IF then on -60k)
Change AVG / E0 settings you change this filter width
NanoVNA Eddy v0.5 firmware use 5k IF (my fw for H/H4 use 12k IF) and not allow change filter width (my firmware allow select it), so you also see 2 peaks (additional mirror IF at -10kHz) on H.
For measure crystal need connect it between NanoVNA ports. Then main frequency correct sweep in measure range, pass thru crystal, and measured. Main problem on measure low width filters like crystal need use less width internal filter.
This my measure series connection 4MHz XTAL between ports, as can see exist strange result - this from wide RBW on measure, but i can reduce it (by increase AVG), as can see 5x avg better, but not good, select 10xAVG and get good result.
If you want use VNA like SA, need use step depend from internal measure filter width.
Additional Lite allow (in last fw) measure and show raw data (CONFIG->EXPERT SETTINGS-> DISPLAY SAMPLES)
in this mode channel data contain raw data samples, and you allow see on diaplay it:
I send to 1 port 30MHz (and stay on 30MHz CW in raw samples mode) and see IF samples on port (in linear format).
Additional i can enable FFT and see spectre (DISPLAY->TRANSFORM->TRANSFORM ON) in Logmag
Now i can see signal SA in frist 512 points
This mode also used for debug, and not friendly use.
PS gf correct answer how all work