Changing code with ( ) when author updates their post (TinyMCE)

Technically, this is an issue with TinyMCE, not with WordPress, but WP does provide a gateway to TinyMCE, which allows you to change settings. Your solution might look something like this:

add_filter ('tiny_mce_before_init', 'wpse303889_tiny_filter');
function wpse303889_tiny_filter ($in) {
  $in['entity_encoding'] = 'raw';
  return $in;
  }

Setting the entity_encoding filter to ‘raw’ supposedly allows you to get rid of spaces being converted to &nbsp, but I have not tested this.