Many MacBook Pro models have two graphics systems – an integrated graphics processor and a discrete graphics processor – and a software feature that optimises graphics performance between them.
On these computers, the "automatic graphics switching" option is turned on by default to allow your computer to automatically switch to the best graphics system for the applications running on your computer. Using this option may also maximise battery life.
If you want to use the higher-performance discrete graphics processor at all times, choose Apple menu > System Preferences, click Battery, click the Battery tab, then untick the automatic graphics switching box. In macOS Catalina 10.15 and earlier, this setting is in Energy Saver preferences.
If you connect an external display to your Mac, your computer will use the high-performance graphics processor until you disconnect the display.
If you can't change graphics settings
If you can't see the automatic graphics switching option, your computer only has one graphics system.