Several essays we read for Wednesday mentioned that post-truth is nothing nascent and has existed for decades, or even hundreds of years. Looking deeper into the statement, it suggests that the soil for the post-truth to grow is always there but something in our modern world allowed it to dominate our time.
Looking at 1989 Tiananmen Square Protests, rumors and distorted truth never ceased to exist among student protesters and elites. Before the protest, the social environment at the time unfavored students due to the social reform happening, causing students to feel unsettled about their life and future. However, without realizing the social condition, some leaders in the government believed that such large student movement must have support from foreign countries with viscous intents.
While among students, as the movement continued and gained momentum, lots of rumors appeared among and outside of the protests due to the lack of effective communication devices. For example, students once gathered in front of the Great Hall of the People believing one of the top leaders promised to have a conversation with them, while in reality, the leader never made such a promise. Post-truth were not a term at that time, but people in a disarray environment tended to believe what they needed to justify the condition instead of what is actually happening in front of them. They also had few ways to testify the fact and rumors due to the limited time, resource, energy at the movement.
However, after the protests, post-truth probably still existed in some degree but was not a severe social issue anymore. It seems like when the chaos and violence passed, the load of information people needed to handle decreased and no urgent issue required them to make up their minds in a short limited period of time.
Looking at the environment we live in today, we are in the age of information overload. Thousands and millions of information are produced every single day. Although we do not face threatening conditions like what students during the protesters faced, but we do need to constantly choose what to believe and how they affect our ideologies/world views.
The booming of social media on the other hand did allow us to have larger conversation with more people. Before it existed, we mostly build consensus among a small group of friends, but now, you can find tons of people who share your opinions and build up on it. On the one hand, it may bring new ideas that create positive social changes but also reinforce the rumors and false facts. Maybe it is why post-truth becomes such a popular term around 2016 when social media has become so integrated into our life that we must finally admit that their influence is not only online, but also in our lives.
Politics of Media 
I like your bringing together of post-truth and digital activism, as it articulates a possibly interesting claim: that they are the positive and negative of the proliferation of perspectives on the internet. On one hand, being able to communicate outside of what is controlled by the state (ie, on tech platforms) has allowed many activist movements and uprisings to organize. But proliferation brings with it the possibilities of other communities and movements forming, like QAnon and other extremist groups, as well as other formations not on the axis of social action. While activism and extremism have existed beforehand (as you point out in your post), a lot changes with digital distribution. Could we imagine an internet where activism can exist without post-truth coming hand in hand? Perhaps one where communication is not largely mediated by for-profit social media platforms utilizing automatic-algorithmic curation which relies upon maximizing engagement, interaction, and length of time on the platform.
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