While looking for some HDMI-to-RCA converters I found out that most of them are simple cheap cables from China without any conversion circuits
Kebidu 1m Wholesale 1080p HDMI Male to RCA Male Adapter
HDMI to 5RCA Male to Male Video Audio Cable Converter Adapter Cable
HDMI Male to 3 RCA AV Cable Lead 1080P HD Convert Line
ELEC 5ft HDMI Male to RCA Video Audio AV Cable Adapter for PS3 PS4 Xbox One Wii
They come in various forms, from component only, composite + audio to component + audio
Many of them have description like this
This cable functions as a signal transmitter, but NOT a signal converter.
As HDMI carries digital signals while RCA carries analog signals. In order for these two formats of signal to communicate with each other, both input and output devices needs to support the signal conversion function (code and decode), please kindly check with your user manual. If both input / output device do not support signal conversion, a signal conversion box is required.
That’s highly strange because AFAIK HDMI doesn’t support analog signal transmission, and indeed it’s doesn’t
HDMI can only be used with older analog-only devices (using connections such as SCART, VGA, RCA, etc.) by means of a digital-to-analog converter or AV receiver, as the interface does not carry any analog signals (unlike DVI, where devices with DVI-I ports accept or provide either digital or analog signals).
Cables are available that contain the necessary electronics, but it is important to distinguish these active converter cables from passive HDMI to VGA cables (which are typically cheaper as they don’t include any electronics). The passive cables are only useful if you have a device that is generating or expecting HDMI signals on a VGA connector, or VGA signals on an HDMI connector; this is a non-standard feature, not implemented by most devices.
https://en.wikipedia.org/wiki/HDMI#Legacy_compatibility (line break added by me)
From the last part above it seems that there are some monitors that accepts HDMI signals in the VGA port, so no conversion is needed. But the cables I found are all RCA and component ones, not VGA, thus need some converter.
Even if passive HDMI-to-RCA devices exist, how do they map the HDMI pins to the RCA pins?