Said Achmiz comments on What are reliable ways to make a statement in such a way that I will be able to prove in the future that I had made that statement?

[Said Achmiz]

I guess the best way is just to post on a bunch of platforms and have those web pages back-up by various archiving services (notably the Wayback Machine).

Note that you can also set up your writing to be automatically archived via archive.is (example).