What do you use to document your home lab?

My home lab has a mild amount of complexity and I'd like practice some good habits about documenting it. Stuff like, what each system does, the OS, any notable software installed and, most importantly, any documentation around configuration or troubleshooting.

i.e. I have an internal SMTP relay that uses a letsencrypt SSL cert that I need to use the DNS challenge to renew. I've got the steps around that sitting in a Google Doc. I've got a couple more google docs like that.

I don't want to get super complicated but I'd like something a bit more structured than a folder full of google docs. I'd also like to pull it in-house.

Thanks

Edit: I appreciate all the feedback I've gotten on this post so far. There have been a lot of tools suggested and some great discussion about methods. This will probably be my weekend now.