Hi there,
So ,sorry I don’t know who “OTHERS” are but that code won’t work…
You can’t do it that way. (do you have compiler output of this code)?
first 3 lines and the last 10 lines b4 it uploads? Verbose output.
I’m sorry , but over “weeks” seriously not trying to be a tool but It doesn’t take that long, Show the picture of it connected and then show the software you are trying to use, nothing you post makes much coherent sense, mixing in what worked and adding the other is just more confusion for you.
Please : POST a picture and Post a code example you can successfully upload to the device. Serial terminal----> USB_C (Xiao)(pin6 & 7)----> Display Device.
START there. Do you know what string to send to the display ?
Does it have it’s own POWER?
HTH
GL 
PJ 
So on second glance, I guess you will get the message of “ESP multi pass-through Ready.” LOL? if it’s plugged in. 
but no data.
Finally, the #1 question… do you know what it is? @cgwaltney you want to guess what I would ask next? 