Transparency mode is not separate from the ANC feature. The ANC function originally uses outward facing microphones to capture the noise, those microphones also pickup the other sound as well. While the function can reduce the sound why not reproduce it, and voila the transparency feature is developed and overtime it evovles to something called hearing aid that the human voice is enhanced for a more clear conversation. And it also develops further to a safe feature - adaptive transprency mode, which will automatically lower the volume that have noise level above the 85dB.
As I mentioned in a post about transparency earbuds, Apple did a great job for integrating transparency feature into their headphones, and the AirPods Max is just another headphone owns that reputation. And I was a bit supprised when the AirPods Max's transparency mode isn't as good as AirPods Pro (both 1st and 2nd gens).
On the market you could find a lot of cheaper headphones with transparency mode but they sound "synthesized", muffled, in order to portray the surrounding correctly, a lot of things being involved like SoC, mic integration, hardware and voice processing technology, let's find out which Bluetooth headphones are implemented perfectly.