@TT
Oh you just take this ultra simple example out from context where only purpose was tell that Siglent do not hide things like FFT data length and also user do not need calculate bin resolution because it is also displayed. It was only purpose about this image, and also show there is markers and peak search etc . This was also not my test at all but from Siglent marketing material where just display that hey there is also peak search.
Also here is markers, now for Delta. And instead of dual tone here is used "triple tone"

In this image split window display. Carrier is over display range but not worry, of course level is there just right. Only adjusted so for get more noise level to bottom. 1MHz, AM modulate 1kHz 20%. (As can see (as can see sidebands levels are -20dBc.)

Here full window display, 1MHz, AM, 1kHz, 100% (as can see LSB and USB levels -6dBc.)
It is not SDS1x04X-E what have 8 times better resolution with 1048576 points FFT data length when X-U model have 131072 points what give here with 5MSa/s (5MHz)
5000000Hz/2/(131072/2)= 38.15Hz when X-E model have in same place 4.77Hz.
As can see in images this signal is very easy to SDS1104X-U. This is resolution for 0 - 2.5MHz band. Of course if take 0 - 500kHz FFT like in @TT image then Siglent X-U FFT bin is 7.63Hz.
This table can also show more, also freq etc but I turn these off and only show delta with just only 3 markers for more clear visibility.

In this image tiny bit more challenging case but still without any problem with SDS1104X-U.
Signal 325kHz sine, carrier level
-40dBm. AM modulation with
100Hz. Modulation depth
0.2% using -40dBm carrier sides need be -100dBm level (-60dBc). Just like checkbox - done.
Also it tell that input channel noise level is not very bad. Using full BW in same setup rise base noise level bit. If you think rise this persistence yellow noise top to -110dBm line it is just there. (note averaging)
This is what you can try...
ETA: Table in Reply #65 corrected. There was error in amount of available memory.
Right is: 1 channel alone on, max 14M. When 2, 3 or 4 channels simultaneously on, all channels have max 7M !