Columns in TCA and DB must be named as snake_case (single_file) instead of lowerCamelCase (singleFile).

'columns' => [
    'single_file' => [
        'exclude' => true,
        'label' => 'Single file',
        'config' => [
            'allowed' => 'common-image-types',
        ],
    ],
    'multiple_files' => [
        ...
    ],
]