Yes, IBKR Pro and IBKR Lite margin accounts are subject to the PDT rule even if you currently do not hold a margin loan.
You can find an Overview of Pattern Day Trading ("PDT") Rules on the IBKR website.
Am I subject to the PDT rule if I am not currently using margin?
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Why am I still a pattern day trader (PDT)?
Will I be subject to the day trading requirements if I open a new margin account?
How much should I fund my account to avoid the Pattern Day Trading Restriction?
Are IBKR Lite accounts subject to the Pattern Day Trading (PDT) rules?