Views menu > Adaptive Degradation Toggle
Keyboard > O (the letter O)
When on (the default), the Adaptive Degradation Toggle supersedes the adaptive degradation that can occur when you transform geometry, change the view, or play back an animation in a shaded viewport. In this case, the geometry remains shaded even if that slows down viewport display and animation playback. Animation playback might drop frames if the graphics card cannot display frames in real time.
Turn off the Adaptive Degradation Toggle if you have large models you need to navigate around and if you are finding performance sluggish.
Adaptive degradation causes shaded objects to be replaced by a quicker display mode. By default, shaded objects are replaced by their bounding boxes.
You can change the display option, and set other adaptive degradation parameters, on the Viewport Configuration dialog (Customize menu > Viewport Configuration > Adaptive Degradation panel).
Note: When you use arc rotate in a shaded viewport while the Adaptive Degradation Toggle is off, objects degrade to bounding boxes regardless of the adaptive degradation settings.