twig check if image style or view mode exists I have a site design the i need to implement. 
in this design I have a grid and in the grid I can put any content (node/paragraph) that i choose. 
the image of the content changes size and ratio in relation to its location in the grid. 
I created display modes for the nodes and i use twig tweak to render it in the right display mode for example:

{{ drupal_entity('node', content['#node'].id , 'box_grid_1x2') }}


for the paragraphs I add my image style directly in the paragraph template:

{{ content.field_image.0 | merge({'#image_style': 'box_grid_1x2'}) }}


because its a little more dynamic than this and my 'box_grid_1x2' is actually a variable that can be set by the user I want to verify that my image styles of view modes do exist before printing them and if they dont I want to print a fallback display\image style.

how would you do it?
Thanks for your help.
You can check image style existence in a preprocess hooks like follows.

$variables['image_style_exists'] = (bool) ImageStyle::load($style_name);


Though it's better to validate user input instead.
Note that configuration entities like image styles or views can be selected through entity reference field which may perform such a validation for you.