I will start with the noise*. Up to 600w and room temperature of 30c, the fan does not exceed 1000 RPM, which practically makes it silent.
Also, it does not have coil whine. I was a bit worried because some gold and titanium ones had it, but I couldn't find anything about platinum ones from Seasonic.
Personally, I decided not to disable the fan at low speeds because at 450 RPM, it doesn't have any audible difference compared to being off. The funny thing is that I bought it for passive operation, but ended up not using it.

As for electrical noise, from measurements I made with a digital oscilloscope when the system consumed 220w, I found 26mVpp ripple at 12v, 45mVpp ripple at 5v, and 33mVpp at 3v3. The 12v measurement is incredibly low, while the 5v measurement, although within ATX specifications, seems a bit high and contradicts the report from Cybenetics that I will mention below. Since it is a system measurement, it is possible that some component is causing the noise during operation, so the cause cannot be isolated to the power supply. However, it was expected to observe noise at 12v, as the VRMs of the processor and graphics card consume large amounts of power. If I measure the 5v disconnected from the system, then I have 25mVpp.

The positive thing about such stable power supply is that the processor is stable with less current. Specifically, with a Ryzen 3600 at 4.05GHz on CCX0 and 4.025GHz on CCX, I lowered the voltage from 1.2V to 1.1825V, resulting in 5W less power consumption and 2 degrees Celsius lower temperature. The total system power consumption dropped from 255W with the previous power supply to 223W or 218W with the voltage reduction on the processor using this one.
Also, it should be noted here that the previous power supply was not some "cheap" one.
I was using the Enermax FMA II 535w for the past 14 years! (purchased in 2006 for 80€)
In 14 years, it is the only component that remained common in all 4 computers I have built so far. In other words, it more than made up for its cost, something I expect from the SSR-850PX as well.

For those looking for a detailed review of this power supply, check here: ftp://members.cybenetics.report/PDF_Reports/d/cybenetics_ehG.pdf
I believe it will be very useful as it was not easy to find a review, and this report played a crucial role in my decision to make the purchase.

Purchase price: 173€

*Greater efficiency, hence lower thermal losses, resulting in less need for cooling and as a consequence, less noise. The lower energy consumption is not a significant reason, as in Greece we have cheap electricity compared to other countries, and the premium one pays for platinum over gold or bronze takes years to pay off.