What systems or tools work best for documenting whole environment configurations?

Today, I added a variable to our environment. I needed to configure a special conditional access policy for one user out of like 200. I know there is a low probability I will remember making this change in 12 months if it causes some issue, let alone the rest of my team who isn't aware of the change. So I'm trying to figure out the best way to document it. This is a topic I've been struggling with for a while, actually. I don't want to write so much I can't find anything, but I don't want to write too little either. We've grown to the point that one person can't keep the whole environment in their head anymore. It's also important to document it because we need to be able to report it, in case a cybersecurity questionnaire asks us, for example. So is this info best documented in a user spec? Master spreadsheet? Pulled from a powershell script? Whatever solution I choose, I will need to remember to update it/account for it every time the environment changes. That's a challenge and basically, none of these solutions are very useful unless I can be sure they are current. How do you guys do it?