How to LOCK/BLOCK selected row in table to be ReadOnly? Is it possible to LOCK completely or make READ-ONLY where id = value in MariaDB?
or add some trigger locking if someone is trying to update selected row ?

Some people says:
"Trigger is not a good way to prevent update" .... well, just because MySQL/MariaDB allow you to do it and it is the easiest solution I decided to use/create one as follows:

CREATE TRIGGER `my_trigger` BEFORE UPDATE ON `my_table`
    FOR EACH ROW IF NEW.locked THEN
    SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'You are not allowed to change 
    this record, please contact your_administrator';
    END IF


As long as it does the job .... i'm happy.
If there is any "against" please let me know.
When would you unlock it?

A typical pattern is:

BEGIN;
SELECT ... FOR UPDATE;
scratch your head, then eventually
UPDATE that row (or not)
COMMIT;


That keeps anyone else from messing with the row, but they can read it.  It's not quite "ReadOnly", and the "lock" is released at the COMMIT.

If this does not suffice, please describe your use case more thoroughly.