As pointed out before, cheap Chinese "Green-Black USB-RS485 dongles" are cheats: what's the point in using an RS485 driver when driving just "ones" and replacing "zeros" with a bias circuit?

I decided to make another small board and order from @oshpark's excellent prototyping service.

This RS485 adapter even has an "echo" switch, which makes using RS485 for the STM8 eForth two-wire interface possible.

Using it as a simple RS232-TTL adapter for 3-wire or 2-wire configuration is also a configuration option. More details are in theRS485-CH340E repo on GitHub.