Hot to get ID of record inserted using model "save()" method

save() doesn't return the ID but insert() does (comment in Model.php actually notes "call insert directly if you want the ID or the record object"). If you must use save you can use the query helper method "$db->insertID()"
https://codeigniter4.github.io/userguide...lpers.html

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Oops, just read your final comment! You should be able to access $model->db because the model class has a magic __get() method to pass through.