I know this is old and other comments have it right- it’s a togglable mode. And while I know it feels comfortable coming from unity - I would highly recommend getting comfortable with blenders default navigation, for example selecting an object and using ‘numpad .’ to focus it. The navigation methods blender uses is way more efficient for modeling while unity’s navigation is better suited for moving around large 3d spaces.

Ideally your individual blender projects should be much smaller than a full unity scene. Think of it less like flying around the 3d space but instead having your model sitting on a potter’s wheel and spinning it around.

Pressing shift+~ lets you navigate that way. Unfortunately you can’t do much in this view, but if you click it will set the camera position, so you can at least use it for navigation. https://docs.blender.org/manual/en/latest/editors/3dview/navigate/walk_fly.html

And here I was hoping I could blender navigation in Unity and everything else. Every app has different movement controls whether Unity, Unreal, 3ds max, or Maya. You get used to it all after a while.