buildForm() method queries the database and returns data which is used to calculate default values for the form. How can I use these values in
submitForm() without querying the database again?
$form_state object can be used to stash that data.
$form_state->getStorage() references a simple array that you can put whatever you like inside, which you can then retrieve in
submitForm() the same way.
You can store values in
buildForm function as follows
submitForm function, you can retrieve this as
$value = $form_state->get('variable_name');
variable_name can be any name