something along these lines i guess (though unless you are only accepting COD type order , removing transaction id’s may not be a good idea , but up to you of course)

add_filter('wppizza_filter_transaction_details', 'my_custom_transaction_details', 10, 3);
function my_custom_transaction_details($tx_keys, $type, $order){
/*
get selected (filterable) parameters
available keys:
[wp_user_id] [order_update] [order_delivered] [notes] [payment_gateway] [payment_status] [user_data]
[ip_address] [order_date] [order_id] [payment_due] [pickup_delivery] [payment_type] [payment_method]
[transaction_id] [total]
*/
/* example : adding order id */
$tx_keys[] = 'order_id';
/* 
example: removing transaction_id 
(wppizza version <= 3.13.1)
*/
$_keys = array_flip($tx_keys);//flip key/value
$_txid_key = $_keys['transaction_id'];//get key for tx_id
unset($tx_keys[$_txid_key]);//remove tx id from array
/* 
example : removing transaction_id 
as of wppizza 3.13.2+ you will be able to 
simply do the following instead 
*/	
unset($tx_keys['transaction_id']);
return $tx_keys;
}

you can change it if you want, but you’ll probably make it unnecessarily complicated for yourself to find an order in your mollie account if any question regarding payment’s should ever arise

all up to you though