Hello Reiza, Hong Kong and Taiwan are included as selectable (thank you very much btw). These have their own motorsports federation to assign licenses for representation on the international stage. There's been Hong Kong drivers and Taiwan drivers that's not racing as China but as their autonomous territories. But Macau is one of these as well, and features one of the most famous event, the Macau Grand Prix and it's absent as selectable on your nations list. I race was Taiwan and I have a friend from Macau who is sad to see it not be an option in AMS2. Can this be included as an option please for a future update? Here's the Macau flag. Thank you.
I believe it will not be added due to political issues. Like Taiwan, China might not also recognize Macau as its own independent territory, so adding Macau to the game may anger China as they may see the action as an act of recognition.
Automobilista 2 has Taiwan (although not the flag graphics). I know because I race as Taiwanese in racing sims. And I use Taiwan in AMS2 AMS2 also has Hong Kong, if Taiwan and Hong Kong are in AMS2 there's no reason why Macau is specifically excluded. Taiwan is the most contentious by far out of the three.