Module development and code questions

I have created custom module to load records dynamically with Ajax callback in custom block in drupal 10.2. But Ajax callback does not work in custom block, where callback function is written on same custom block file, please see the code below,

Dear Drupal Support Team,

I recently deployed my Drupal 10 website on OVH, making it accessible to the public. However, when I test the form (Webform module) which includes a field for uploading a file, upon clicking the 'submit' button, an error appears on the page: Error 503 Backend fetch failed. Guru Meditation: XID: xxxx Varnish cache server.

The form is a 'Webform' module in Drupal 10. It was working correctly in my local environment; I was able to submit the file without any issues. However, now that it's in production, when I test it, I encounter this error

Dear Drupal Support Team,

I hope this message finds you well. I am reaching out to report an issue I'm encountering with the RSS feed generated by our Drupal site, which is affecting its appearance on Google News.

I have successfully published our site on Google News following all the required procedures. However, upon further inspection, I have discovered that the RSS feed generated by the Views with Feeds module is encountering validation errors. These errors are preventing our site from appearing on Google News.

Greetings,

I am reading up on the Cache API, and have a question about caching users (or objects in general) in the DB, i.e. the cache_default MySQL table.

Please consider the following simple function to retrieve a User object (I know this type of code should probably live in a custom service, but am using a function here, just for clarity):

So we have our oembed podcast player which works on websites if they have HTML editor.

However we have a client who uses Drupal and we would like to officially support the community. 

I have downloaded the Soundcloud media module - which is awesome start for us, as we can rip it apart and build the parts that we need. However I am wondering if anyone has skill set in working media and modules. Is there any well documented how-to develop for this area of the Drupal system?