This is example about how it need work. (This is not made using Rigol)
In this test example used samplerate and scope input sinewave frequency as:
fNYQUIST/1.82 (equivalent as with 1GSa/s and 275MHz )
This image is just for imagine continuously running and Sinc off. (Of course not Rigol)
Rigol do (roughly) this kind of Sinc if we think there is dot middle of each line. If these imagined points are used for Sinc (draw via sample points rule) we can see very close what Rigol "looks like" do. (who knows how it really do but it looks like it in my some old tests)
Same running but now dots. (NO Sinc)
(note: last singlle acq dots bit more bright)
Then single shots. In all next three images sampled data is same for show that it really draw via real sample points.
ADC sample dots.
Lines Sinc (Sin(x)/x) off. (draw exactly via ADC sample dots.)
Lines Sinc on. (draw exactly via ADC sample dots.)
(pity it do not show these real sample dots here)
This is how oscilloscopes need do Sinc. (and all serious oscilloscopes do, look Keyshit, look Tektronix, look Siglent, look R&S, look Goodwill.
Note that Sinc is good for sine or some other "smooth" waveforms. It is NOT best in all cases for fast square-rectangle types of signals. Later when I have time I will show some these things but not in this thread for avoid too deep off topic.