One of the problems with this is that there is not general agreement on what constitutes, "propaganda". The Taiwanese official cited in this article refers to

One of the problems with this is that there is not general agreement on what constitutes, "propaganda". The Taiwanese official cited in this article refers to it as, "disinformation" and many people wrongly assume that the government is referring to "fake news" or factually false information when it refers to propaganda. In fact, many governments and other organizations in a position to distribute information arbitrarily refer to any information that counters their narrative as "propaganda" whether or not its factually correct. You can be certain that the Chinese government regards any accounts (let alone praise) for the Tank Man as hostile propaganda, no matter how factually accurate it is, just like the US government treats narratives that reflect negatively on the US government narrative to be propaganda ("sowing dissent"). I'd be more much receptive to a system that had a way to flag information as "factually inaccurate" (as difficult as that may be) than a system that flags messages as "propaganda" which is far more arbitrary and subjective standard.