Twisted Pair Communication Wire

What protocol? What speed? What UART? What cat wire?

Not exactly sure what you mean by "simultaneously 1 twisted pair for a dedicated Rx or Tx" ?

Could you do a quick Paintbrush sketch?

Is this single-ended serial data or differential?

I have, for many years, successfully used two twisted shielded pairs for single-ended serial data where Tx and return (gnd) and Rx and return (gnd) are on separate twisted pairs even though the returns for each are electrically common.

I have seen single-ended serial data on a shielded twisted triple, and it works, but I'm not really a fan, especially if there is a chance that the link might be configured as full-duplex. Plus, STT is harder to find than STP for those who love abbreviations.