2
The easiest to resolve (and most likely) issue is:
You are limiting the allowed HTML tags for the text format you're using and you haven't allowed the align (and also caption, if you want captions) attributes for the drupal-entity HTML element. (I'm assuming you do have the Align images and Caption images filters enabled because you said those features were ...
1
A file that comes in from a browser's Web API as a Blob is probably base64-encoded. PHP will not decode files in the POST or GET parameters. It is up to the PHP application to decode the file before saving.
if (!empty($payload['blobFile'])) {
$name = str_replace(' ', '_', $payload['fileName']);
$file = file_save_data(base64_decode($payload['blobFile']), ...
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