Quite a lot, as we always document all the clients processes.
I would say 10% of the project duration is documenting atm.
So usually we use whatever system the client already has, notion, google docs, jira, miro etc. Different use case my require different systems within the same organisation. Important to have a change log, easy access for all stakeholders, and a refresh at least once a year. There must be some AI solution coming soon on that.