Are you using the Mixer Configurations? Are you constantly resizing the mixer? I think Nuendo 5 was the last version that kept everything visible by default. That is still sorely missed here.
You can assign key commands to open/close the various mixer sections. You can switch between the mixer and the project page using control + tab. If you aren’t using the mixer configurations you should start. Assign them to key commands and take control of your mixer!