One of the ways would have been Letters to the editor, which were basically blog posts written by individuals who are not journalists, published in a newspaper. Of course the editor had to approve of what you had to say so it wasn't a perfectly free medium.
These existed well into the 20th century even into 1990s.

Going back in past there was the option of nailing pamphlets to churches, however this was highly dependent on having friends with a printing press which was the cutting edge technology for the time.

We used to have Op-Ed sections in newspapers and they used to be literal sections, and lots of people would mail opinions in and hopefully make the cut, and in internet's not-quite-still-an-infant age, BBS used to be used to such an effect as a blog a lot of times, but nothing was ever on the scale of being able to easily broadcast your thoughts to the world unless you were significant enough

I know the private version is basically a journal or diary, but I’m not as sure if those were sometimes more publicly shared in the past or not.

Prominent figures often had their journals and diaries and letters published by others, but usually that happened after they were dead.