They just disagree on who should run the reunified nation.
We both know, that you do not agree that the moon is made of cheese, in this situation. I have just made words come out of your mouth, to something that you do not agree with.
To say that they "agree" is just a silly word game, that does not reflect the truth of the matter, and instead is playing into propaganda that denies the reality that Taiwan is already a country, and is already independent of china, and that Taiwan is not interesting in being taken over, or taking over china.
Taiwan is a democracy and a majority of Taiwanese want independence but argue for keeping the status quo in order to avoid a war (both the KMT and the DDP - their disagreement is more technical than that). Some wanted Taiwan to declare it in the 90s to force the hand of the USA and win a decisive war but this position seems more precarious nowadays.
At any rate, summing it up as "the RoC agrees" would seem to simplify a cultural argument along the lines of "the US agrees completely that guns are good".
For example: https://www.scmp.com/comment/opinion/article/3151551/tsai-in...
> On Sunday, at an event marking the same revolution, Tsai called on the Taiwanese people to renew their commitment “that the Republic of China and the People’s Republic of China should not be subordinate to each other.
https://www.washingtonpost.com/world/2021/10/10/taiwan-china...
Tsai has not made this one country position part of her administration, and her speech a couple of days ago made that even more explicit.