SQL & PL/SQL

Hi I'm doing some manually locking row in Oracle SQL for Oracle APEX, i use some AI to help with this but i have a feeling that I'm being bamboozle. I also read the docs and make a table to compare different kind of lock to be honest I don't really think i understand it. Here a table that i think each lock kind does:

Here is my SQL:

declare
	l_old_sr_co_owner_list apex_t_number;
begin
	-- row locking i'm assuming this is 'SS' lock
	SELECT
        srco.id__employee
    BULK COLLECT
    INTO l_old_sr_co_owner_list
    FROM
        my_schema.request                        req
        LEFT JOIN my_schema.request__employee__sr_co_owner srco 
        	ON req.id = srco.id__request
    WHERE
        req.id = :p18_id

    FOR UPDATE;
    -- doing modification on request and request__employee__sr_co_owner
end;

what i think this lock is doing:

• Don't allow update, delete to request where id = :p18_id.
• Don't allow update, delete to request__employee__sr_co_owner where id__request = :p18_id.

what i want additionally which this lock is not provide:

• Don't allow insert on request__employee__sr_co_owner if id__request = :p18_id.

the AI is raising some issue that I not sure about:

If a request currently has zero co-owners, the LEFT JOIN evaluates to NULL for the child table, and locking behavior on those non-existent child rows can become unreliable or fail to prevent concurrent inserts into the child table. (This sound like non-sense to me but I'm not sure)

Bellow this code i also doing some prevent loss update so maybe locking request__employee__sr_co_owner is not necessary

    -- prevent loss update
    WITH sr_co_owner AS (
        SELECT
            id__request,
            LISTAGG(id__employee, ':') WITHIN GROUP(
            ORDER BY
                id__employee ASC
            ) AS id__employee
        FROM
            my_schema.request__employee__sr_co_owner
        GROUP BY
            id__request
    )
    SELECT
        CASE
            WHEN utl_raw.compare(
                standard_hash(req.sr_owner__employee
                              || '-'
                              || srco.id__employee, 'SHA256'),
                hextoraw(:p18_hash)
            ) = 0 THEN
                '0'
            ELSE
                '1'
        END AS loss_update_status
    INTO l_loss_update
    FROM
        my_schema.request req
        LEFT JOIN sr_co_owner          srco ON srco.id__request = req.id
    WHERE
        id = :p18_id;