Let me clarify for those who do not have the insight into MSFS tech.
In simplified terms MSFS offers several technologies to implement aircraft systems. And for these technologies there are different APIs.
The two main ones are Coherent (Javascript) or WASM (compiled languages, mainly C++ or Rust).
Unfortunately these APIs do not offer the same functionality and also each has its own bugs and quirks.
In this particular case the Coherent API does not provide the required data for the FSLTL traffic (see bug report above). As the FlyByWire A32NX implemented TCAS in Coherent JavaScript it currently does not “see” the FSLTL (or any AI) traffic in the air
WASM build TCAS system do not seem to have this issue.
Hope that helps.