The “Include new, eligible accounts automatically” option allows Chase to send Plaid new accounts from their API, but it doesn’t add these accounts to the user’s Item.
When Plaid detects the presence of new accounts, a NEW_ACCOUNTS_AVAILABLE webhook will be fired to notify you that there are new accounts available to be linked.
To add these new accounts to their Item, the user will still need to permission them by going through the Account Select flow in Link’s update mode.
In summary, the “Include new, eligible accounts automatically” option allows Chase to send Plaid new accounts, but to actually add the accounts to their Item, the user will need to select them by going through the Account Select flow in Link’s update mode.