Command/ThemeAssetsInstallCommand.php
private function _absoluteSymlinkWithFallback(string $originDir, string $targetDir): string
    {
        try {
            $this->_symlink($originDir, $targetDir);
            $method = AssetsInstallCommand::METHOD_ABSOLUTE_SYMLINK;
        }
        catch (IOException $e) {
            // fall back to copy
            $method = $this->_hardCopy($originDir, $targetDir);
        }

        return $method;
    }
private function _absoluteSymlinkWithFallback(string $originDir, string $targetDir): string
    {
        try {
            $this->_symlink($originDir, $targetDir);
            $method = AssetsInstallCommand::METHOD_ABSOLUTE_SYMLINK;
        }
        catch (IOException $e) {
            // fall back to copy
            $method = $this->_hardCopy($originDir, $targetDir);
        }

        return $method;
    }
Try to create absolute symlink.
Falling back to hard copy.

@param string $originDir
@param string $targetDir

@return string