How we can fix Fatal error: Uncaught Error: Call to undefined function xdebug_disable() error?

it can be happen when you want to install xdebug. you can simple remove xdebug and all thing worked perfectly or not you can change Magento core code.

find vendor/magento/magento2-functional-testing-framework/src/Magento/FunctionalTestingFramework/_bootstrap.php file and, find below codes

if (!(bool)$debugMode && extension_loaded('xdebug')) {
    xdebug_disable();
}

Now, you can change the code like this.

if (!(bool)$debugMode && extension_loaded('xdebug')) {
    if (function_exists('xdebug_disable')) {
        xdebug_disable();
    }
}

also, here is a git link to install xdebug correctly.