As mentioned above, there is a workaround. I've had mine linked for years.

You set it up as a new bank account in QBO - make it a cash account.

After the account is linked, go back into QBO and change the account type / name to the correct other liabilities / Line of Credit and save.

Just pay attention to exclude transactions that are already entered in your checking account so they are not double counted.  (like bank fees)