CPT EVENT – listing by month and filtering by category and month – form select option

Problem solved!

Before – Select Month

<option value="01"></option>
<option value="02"></option>
etc.

Change – Select Month

<option value="20210101"></option>
<option value="20210201"></option>
etc.

//ARGS
$selected_cat = $_GET['cat']; //category value
$start_date = $_GET['month']; //month value
$end_date = $start_date + 30;

'meta_query' => [
[
'key' => 'event_date', //acf date picker field Ymd
'value' => array($start_date, $end_date),
'compare' => 'BETWEEN',
'type' => 'DATE',
]
]