Reunite is propaganda because it gives credibility to the lie that these two countries are and/or were one like for instance Germany after world war II.

Taiwanese do not see themselves as Chinese, just like Ukrainians do not see themselves as Russian even if they speak the language. By playing along you are effectively carrying water for the Chinese. That may be your goal, but then you should be clear about that. If that is not your goal you should refrain from adopting the language of the party that is clearly the aggressor here. The 'ROC' moniker stems from a bunch of Chinese that fled there in 1949 after they lost their struggle with the communists inside China. They ruled Taiwan and they named it 'Republic of China', a name that has caused a lot of confusion with those unfamiliar with where it came from.

This is the reason the Chinese now lay claim to Taiwan, and it is about as misguided as it gets. They got Hong Kong by being patient, they may take Taiwan by force.

If you are playing into their hands by parroting their terminology you are fractionally helping to normalize their behavior towards Taiwan. If it should come to pass that China will take Taiwan by force that will have grave consequences, for the Taiwanese, the Chinese and the rest of the world as well due to the central spot that Taiwan occupies in the global supply chain.