At the end of the day some of this information is most likely lodged in your brain and the digital version can be discarded. However some of it should be retained manually in some system - or at least I feel it should.
What approaches do people use to consolidate and store this information to allow all tabs etc to be closed for the next work day?
Mostly it's just bullets. If a bullet is critical I'll prepend it with !!!. If it's a task, I'll use * instead of - for the bullet marker (then move the task to my separate task tracker later - notes doc isn't good for long-term task management)
If I want to tag the note explicitly with a "tag", I'll add one in brackets - but honestly these aren't that helpful.
Ctrl-F will generally find what I need. Aside from that, what's mostly been helpful is the dates - I often remember roughly when I learned a bit of information, so if I can't find it with Ctrl-F, I'll scroll back to that "era" and look around.
Pay a lot of attention to yourself when you're looking for historical information: what do you search for? Are there key things you often look up over and over? If so, what search terms did you use when trying to find them? Add those explicitly to the entry, so next time you'll find it easier.