Leave details empty and click Create:

Code below:
public static function form(Form $form): Form
{
return $form
->schema([
Forms\Components\TextInput::make('field1'),
Forms\Components\TextInput::make('field2'),
Forms\Components\TextInput::make('field3'),
\Icetalker\FilamentTableRepeater\Forms\Components\TableRepeater::make('details')
->relationship('details')
->schema([
Forms\Components\TextInput::make('field4'),
Forms\Components\TextInput::make('field5'),
Forms\Components\TextInput::make('field6')
->hidden(fn (string $operation): bool => $operation === 'view'),
]),
]);
}