You can use CloudLinux Selector to enable GD extension in PHP via Plesk.
1. Log in to your Plesk account.
2. In the right-hand sidebar, click on PHP Selector.
3. Click on the Extensions menu.
Note: If the Extensions page shows an error related to the native PHP version, change it to a non-native version first.
4. Tick mark the GD Once enabled, it will display a success message.
The message will read that the module GD is saved.