I use markdown text files which are synced to my nextcloud instance.
This is somewhat tangential to your post, but I think using infrastructure as code and declarative technologies is great for reliability because you aren't just running a bunch of commands until something works, you have the code which tells you exactly how things are set up, and you can version control it to roll back to a working state. The code itself can be a form of documentation in that case.
Some examples of technologies which follow that paradigm are docker compose, ansible, nixOS and terraform. But it all depends on your workflow.