IBKR does not act to automatically convert currency balances back to the Base Currency as this action would require assumptions as to the account holder's desired currency exposure as well as the trade price at which they would be willing to close the position.
The IBKR Universal Account allows you to hold cash balances and positions denominated in multiple currencies, which can be viewed in the Account Window of Trader Workstation or the Positions page in Client Portal
However, there are limited exceptions where IBKR will automatically convert non-base currency balances.
Additional Information: