For keeping strict code snippets, I use SnippetLabs, so I have syntax markup to help visualize code better. Any snippets I keep here are copied regularly to a static text file (for backup locally and on cloud), and project-specific READMEs (to help devs). I'm also getting into using VSCode snippets since I made the switch, but only with stuff I use immensely (like Bootstrap components or basic form elements) - since it requires learning and recalling shorthands (rcc anyone?).
When it comes to notation of process, or documentation of my own, I either keep track of what I'm doing step by step in Trello, write rough notes and snippets in MWeb, or write more loose notes in Evernote.
Trello's great because it supports Markdown, making things like code snippets and headers vs paragraphs more legible. And the fact my team can easily see the tasks I've completed, how I did each step, and replicate them using my snippets is cool. It's crazy simple to pop open a card, write out almost an entire article framework in Markdown, and copy paste that later into a Markdown-based blog or another longer-form text editor.
Evernote is great for jotting down ideas and syncing them across my devices. Although code snippets suck there, things like single quotes get converted to ` for some reason and break when pasted into code editors. I'm thinking of migrating to Markdown files and GDrive eventually, but it's hard to beat the convenience and accesibility of Evernote.
MWeb is great for writing more long form content (dark themes ftw), or translating documentation to a blog article. I also feel more confident placing my snippets/notes into an app that I know I can backup or export data out of, which MWeb makes easy (you can even generate a static blog out of notes - nifty).
When I was learning React: