Hello Giulio.

You can remove the loader by adding this CSS to the page:

.wpdt-c .wpDataTables .overlayed:after {
    display:none !important;
}
.wpdt-c .wpDataTables .overlayed  > * {
    opacity:1 !important;
}

Custom code needs to be applied to the page where the booking form is. Depending on what you're using (Gutenberg blocks, or some page builder), adding the CSS or JS can be done in a few different ways. 

If you need help with adding custom CSS to the page, please take a look at this article.

If you need help with adding custom JS to the page, please take a look at this article.

You're welcome, Giulio, glad I could help.

Please feel free to reach out to us if you have any further questions.