Cycles and Eevee. The reason for a slowdown with Cycles is because it

will keep processing the render continuously.

That might get your CPU (processor) or GPU (graphics-card) usage to

100% load and compromise your computer's performance.

Suppose you want to have a view if your scene with textures and a

rough preview of lights, you can use the Material Preview mode. The

shortcut to quickly change shading modes is the Z key.

Regarding Viewport shading, you can still choose different lighting

modes for the preview and enable Scene Lights and other options. Use

the small arrow on your shading modes' right to change the preview

display (Figure 6.3).

Figure 6.3 - Material Preview options

With Solid shading mode, you have additional options to control

transparency and also use colors from the model for material preview