In the Network Editor you can toggle the overview box with the "O" key. How do you do this in the Viewport?

Honestly, my take is that the viewport “overview” thing just isn’t as slick as in the Network Editor. I usually just hit Home or Frame Selected—quick and keeps me oriented. It’s not a mini-map like in the Network Editor, but for me it’s totally enough to avoid getting lost. Feels simpler, even if it’s not as fancy.

I discovered the solution. If you have 2D Pan & Zoom button active (above viewport) it will show the overview box in top left of viewport. You need to activate 3D Camera button instead of(an may need to click on Reset screen button).