On Wed, 30 Dec 2020 18:31:07 -0000 (UTC), Martin Gregorie
 declaimed the following:

>>
>Ignore the gpio lines: Just get a standard a USB-serial adapter. Each
>supports a single serial line, so get one for each device with a serial
>port that you need to connect to the Pi and either plug them directly
>into the Pi or, if you run out of USB ports, via a USN connector block.
>

 That doesn't answer the OP's actual request -- they want the ports
physically on the R-Pi to be VISIBLE on the host (desktop/laptop) computer
that is connecting to the R-Pi.

 Unfortunately, that likely means a commercial $$$ ($260) package (which
may not be available for ARM architecture).
https://www.eltima.com/products/com-port-redirector/ {STRIKE my
parenthetical: "Linux version for ARM-based devices is available. Now you
can share serial ports on ARM devices or connect to remote devices. Note:
you need D-Bus to be installed on your device to use this version."}
Hmmm... https://wiki.eltima.com/software-licenses/trial-version-eula.html



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