This is very traditional and I do it too with handwritten notes which I expect to let age then mostly discard before filing only the good references in cabinets.
For the typewritten stuff or things which are good references to begin with, I went digital fairly traditionally as I'll explain.
So far no one has been able to convince me there is anything better than a secretary.
As an executive needs leadership documentation, I think it's best to have a full time operator who puts their focused effort on the notes I need taken, the selection & crafting of those to be destroyed, confidential, released, or published as well as their organization, filing, retrieval and backup.
At the opposite end of the spectrum without any staff you want to minimize or eliminate all of these same efforts without fully compromising the advantage you would have if there was a specialist doing this for you.
Even when I am an executive, during a time when I'm making progress at a scientific bench the only way to get complete documentation is to spend at least half the time sitting down to document where you are, instead of making more progress at the bench.
When that sitting-down pose can not be attained for the duration of a project, that's when somebody has to sit down afterward and that's not always the most useful documentation, and never complete enough.
You can get to the point where the only reason to make notes is if you will certainly go back to look at them, or if they are an essential element of otherwise unobtainable documentation.
This may have some similarities to engineering projects where you are sitting down for both the progress-making & documentation-generating efforts. Either way what you need is someone standing there with a clipboard & audio recorder who will type it up and file & retrieve it for you. You can probably imagine how you would be able to leverage such a conventional system better every year.
Without that you are almost always going to have to settle for less-than-ideal documentation, so truly optimize for this instead. Then take a few years to get better at leveraging what you really have to work with.
Until you get a secretary, at least use your PC text editor & file manager as a substitute for their typewriter & filing cabinet.
These are two of the business machine essentials that IBM wanted all offices to be able to use an early IBM PC for instead, as a high-tech alternative. So they offered printers and hard drives, and you should probably still hang out in your file manager yourself if there's no one else doing it for you.
Make yourself a storage partition on a HDD and create your own folder for each subject manually as needed, giving the subject a short meaningful name like a secretary would do on the tab of a real manila folder. Then take notes right into text editors no differently than DOS, and file them into your desired folders manually. There will be a creation date, modification date & access date associated with the files & folders and the text can be some of the most rapidly searchable.
It's OK to make a folder for a single worthwhile text file, since you will sometimes want to search by folder, other times by filename or contained text. Try to stay organized and don't make too many subject folders though in case you want to be able to search them easily manually sometimes. In real filing cabinets there was usually only one layer of subfolders, which are supposed to be much more familiar today but sometimes I wonder.
With 4 primary partitions addressable by DOS, these were supposed to represent the four drawers of a filing cabinet. A common arrangement would have been one drawer with a main folder for each product, one drawer with a main folder for each customer, one containing each month's invoices, and one with each month's correspondence.
Storage for one's personal notes is not usually a large requirement, and you may not need a database to be helpful.
Comprehensive snapshot/backup can be made by easily copying the entire organized partition contents of small universal text files, uncompressed.
Tagging and word processing can always be done after initial note-taking.
If all the notes even turn out to be worth it.
Make it easy on your secretary.