If you are a U.S. person who has submitted a W-9, any U.S. tax reports filed on your behalf (e.g., Form 1099, Form 5498, Form 2439) will be reported in USD regardless of the Base Currency you have selected for your account.
If you are a Non-US person or entity that receives a Form 1042-S, the tax report will be reported in USD regardless of the Base Currency you have selected for your account.
IBKR also offers tax-advantaged account types for clients who are U.S. citizen, such as IRA accounts. Please click here to learn more about these account offerings.