Thanks for reaching in the QuickBooks Community page, @Vel5.

The multicurrency feature gives you the ability to record transactions in foreign currencies. Once turned on, it can't be turned off. This is because the currency conversion information will have to be accounted for in the system moving forward.

To get more details, you can check out this article: Learn about Multicurrency in QuickBooks Online.

The Community always has your back, so please let me know if you have any other questions. I'll be more than happy to help. Keep safe.