I have a more mixed approach.

Decisions or attempts, i try to document them as comments on the ticket. It feels a bit like a conversation with my future self 😄

Things that pop up in my head that I don’t want to forget, but don’t have time to write out, I put in a new tab on nodepad++

Archi things go as markdown in de source code

Investigations and reports in a wiki

All these have all the pros of an engineering handbook out of the box (date, issuer, …)

I only use paper for the stuff I don’t want a trail off and just want to throw away afterwards.