Always publish on your own platform then syndicate it across all the relevant social media providers to get exposure. It's a huge pain, especially now that most platforms are closed and don't provide automation (APIs, RSS), but it's really the most flexible solution. It also makes syndicating to new providers a lot less painful since you'll have some standard raw form (e.g. Markdown) which you can create a manual or…
Standard reminder that Markdown, while pleasant to author in, is perhaps one of the least standard formats ever (every implementation does things their own way; see Babelmark 2) and not a great archive format, largely as a result. (Markdown files don’t have version or flavor information embedded) I hear org-mode is a good alternative. In the mean time, consider storing a permanent .html version upon publication of ma…
If your documents are available on the open web, you can visit them on the Wayback Machine to make sure they're cached as HTML. This is in some ways more reliable, and some ways less, than trying to keep track of your own HTML transcodes over decades. It's generally a more reliable way of making sure they're available after you disappear.