The page you link to is intended for Trading Groups (Institutions and Organizations).Yes. You can setup a sub-account in account management. But you'll need to fund them separately, depositing money separately into the sub-account.
https://www.interactivebrokers.com/en/software/ptgstl/topics/ptgsubaccounts.htm
The page you link to is intended for Trading Groups (Institutions and Organizations).
However, a similar possibility exists for individual (retail) customers at IB. The difference is that all account numbers (Uxxx if you're with IB US) will be listed on the same customer's name.
It’s the same instructions. Go to Account Management and create your sub account.
Or Google:
https://www.google.com/search?q=interactive+brokers+create+subaccounts