It is impossible to help you based on your description as it only states it does nor work for you, for the start copy the query you created.

the query  is in construction mode, in that case I just have to put the name of the table, #__categories, and the WHERE created_by = $user->id, but it does not show me the fields, why it does not give me the info?

Your query is not correct, you need to define text and value properties https://www.seblod.com/resources/extensions/archives/seblod-2-x-select-dynamic-field

I did that, the text=title and value =id, the page gives me an error

SELECT title AS text, id AS value from #__categories 

should work. Otherwise there is something broken on your system.

where do I add the created_by = $user->id?

See

https://www.seblod.com/community/forums/fields-plug-ins/select-dynamic-problem#post60660

but you write that in phpmyadmin or in the field construction?

In neither of these. I have added

// Set
$field->value = $value;

on line 533 and 534 of select_dynamic.php in \plugins\cck_field\select_dynamic. This is for version 3.17.1 (Seblod 3.17.1) If you use another version look in select_dynamic.php and find function onCCK_FieldPrepareSearch. Add the lines just before //Return like this:

// onCCK_FieldPrepareSearch
public function onCCK_FieldPrepareSearch( &$field, $value = '', &$config = array(), $inherit = array(), $return = false )
{
if ( self::$type != $field->type ) {
return;
}

// Init
if ( $field->bool3 ) {
$divider = $field->match_value ? $field->match_value : $field->divider;
$field->match_value = $divider;
if ( is_array( $value ) ) {
$value = implode( $divider, $value );
}

$field->divider = $divider;
} else {
$field->match_value = $field->match_value ? $field->match_value : ',';
}
self::onCCK_FieldPrepareForm( $field, $value, $config, $inherit, $return );

// Set
$field->value = $value;

// Return
if ( $return === true ) {
return $field;
}
}

how do I ad the created by user?, is the only thing I need to complete this so i gives me the values based on the current user logged, the query right now is like this "SELECT title AS text, id AS value from #__categories WHERE parent_id=8" I just need to know how do I make it to show me the info of the current user, it's almost complete

I don't know. The table #__categories has a column created_user_id. You can retrieve those numbers. I don't know how to get the live user out of these.

I tested and there is no bug, everything works correctly - your problem is there is no "created_by" column in categories table, correct query which works is

SELECT title as text, id as value FROM #__categories WHERE created_user_id = $user->id