Check this thread, with the modern changelogs. It has links to 6 other threads with older changelogs.

It only goes back consistently to version 78.1, and sporadically to version 53.1. That covers all the way back to 2011/2012 though, so a huge part of TPT's history. You can find a few other changelogs in the Announcements subforum, but it's hard to find.

Going back to the absolute beginning, that doesn't exist. The first 20 versions or so weren't even on this website. At that time, TPT development got transferred to Simon who created this website. I've never seen a changelog or even code history from before this time so I don't think it was tracked back then.