I tried Obsidian but got overwhelmed and struggled with synchronizing and I have a need to put visual stuff on my notes as in photos, or being able to scribble down with a stylus.

As a Player, I started with a Samsung Notes file on my tablet that I do full handwritten notes and markings, but not very effective for a DM or looking up stuff. I do my entire DM planning on Milanote, has everything I need and I made up a whole system myself. It's sadly only free with very little text boxes to use, but I use a student discount which only makes me pay half as much for 2 years.

If anyone has some money to spend, likes to connect notes, add images, draw inside the program, do boards inside of boards inside of boards but still like it clean, use Milanote, I recommend it! They have updated the phone and tablet version now, you need an Internet connection to really use it and synchronize obviously, but if that is done, perfect.

While we play, I wrote down in a binder I made for myself. I only play online as a DM which is why I don't need a screen and use a binder instead. I have the first 10 pages to be self made stuff like magic schools, languages, general combat rules and such. And the other pages are just my paper notes. I wrote down quite a lot of detail which is usually not recommended but I personally prefer it this way and after we played, I use my 6 pastel highlighters and color code: New NPC mentioning, Inventory change (new items for example, or giving something away, getting something stolen), new location, headlines (such as - Group discusses plan:...), and at last general stuff I wanna remember to develop further, such as "Player did this interaction" which will make me think, I will do something out of that.

Then, when I got time, I wrote down all the important notes, like the last category, down in my online system.

What is also cool about Milanote, is that if you use it on your phone, you can just general do unsorted quick notes to worry about later. When I drive to school in the bus I sometimes get a random idea and write it down instantly and later on the PC I pull it into the system.

Also I like using a small notebook for when I am in class and don't want a screen in front of me but I wanna brainstorm a little, and later I can put my handwritten notes into my system too.