I keep seeing it pop up when researching and wanted to hear from other gardener's about how they manage their garden information. Pen and notebook? Special designs? Online?
Personally, I've never kept anything previously so each year will be a semi-fresh start and daily online searches to find solutions. This year I hope to at least write stuff down; seeds we have, easiest plants to collect seeds from, best/worst companions, harvest time/sprout time, and disease/pest prevention methods.
I'm not very organised on paper but I love my pollinator plants and try to focus on resilience. I have kept every tag from plants I have planted even if they did not survive.
I store my seeds by the time of year that I sow them (vertically so I can sort through quickly enough).
Then I do a walk through with my phone video at different times of year. Between the videos and the photos I have a nice visual reference of what was looking happy in the garden at different times of year.
Lastly I have a insect ID app (Picture Insect) for pollinators and pests. My photos in there and the dates can tell me which plants were good hosts to pollinators, which were harmed etc.
When I started, I meticulously logged everything into a classic notebook. Just things like "planted lettuce", later "lettuce died because of frost", then "replanted lettuce", "first lettuce harvest", "lettuce bolts except variety X", to give examples.
The use of that was that I could look back and see when I went wrong and what I was doing right, facilitating faster learning. Also I could create a monthly to do-list from the entries. I did this for three years.
I used Google tables (practically Excel) to plan the vegetable garden. Seeding and planting times go in one sheet, then one sheet per year, one line per garden row (one meter lines separated by 30cm in my case), into blocks of lines to facilitate rotation. After a few years, I stopped the massive experimenting and cut down to things that worked. The plan is stable since 2018, I modify on the fly, often according to the amount of seedlings I made.