Like the docs say: Insert, update, delete
“You may also use the create method to save a new model in a single
line. The inserted model instance will be returned to you from the
method. However, before doing so, you will need to specify either a
fillable or guarded attribute on the model, as all Eloquent models
protect against mass-assignment.After saving or creating a new model that uses auto-incrementing IDs,
you may retrieve the ID by accessing the object’s id attribute:“
$insertedId = $user->id;
So in your sample:
$user = User::create($loginuserdata);
$insertedId = $user->id;
then on table2 it is going to be
$input['table2_id'] = $insertedId;
table2::create($input);