I am from Hong Kong, I can confirm that Taiwanese flag is not displayed in original Emoji keyboard (still appear in third-party keyboard like kaiboard). I am using HK region apple id and latest ios version
Also I can confirm. Friend of mine was in China and bought iPhone XR dual sim. And now lives at hometown – Moscow, Russia.
Russian interface, Russian region is installed.
But Taiwan flag is completely missing: in chats, web and keyboard.