I have seen people do this in a number of ways:

- Keep everything inside your head and unlock it whenever needed! That's superhuman stuff and definitely not the ideal. - Take verbatim notes or transcribe conversations, store them in GDocs/Notion, and store insights in a spreadsheet (Airtable/Excel/Sheets). - Use a software solution to manage it. This branches out into multiple directions depending on the role - PM, or UX researchers, for example. - Build custom scripts and workflows

What has helped you make sense of user/customer feedback in the past?