LIke they said above… the default is the Windows Fonts folder, but you can browse to any folder on your computer. And any folder can be set as your font directory. If you want to keep the default Windows directory but also be able to navigate to the alternative folder with ease, in any Blender File browser, the far left has had bookmarks for a while. you can browse to the folder you want to add and click on the + sign in that box. There’s also a Recent box at the bottom left that shows files you’ve recently accessed within Blender.