Thanks i have watched the teardown of Siglent SSA3021x and SSA3032x in EEblog and Signal Path a few times, so i have a fair good idea of their design blocks. Both are identical in hardwares. Regarding the phase of spurs in a mixer, this video from Marki livestream explains it but the concepts are "confusing and like a black hole " as described by the speaker:
https://youtu.be/BvaOCW0rUYU
I have also seen a video about zero span from RS channel. I must go to bed.