Can I change home currency in multicurrency option of QB online new account if I have not yet performed any transaction or issued any invoice in QB?

You can no longer change your home currency setup once you've enabled the multi-currency feature in QuickBooks Online (QBO), Srdjan.

During your setup, there is a note before turning on your multi-currency it  said to place the correct currency since changing it won't be possible after establishing your account. I've added a screenshot for reference:

If you still wish to change it to EUR, you can cancel your account and create a new one to start. Here's how:

1. Click the Gear icon.
2. Select Subscriptions and Billing.
3. Choose Cancel on the subscription tile.
   
   

Another important point of that is you can record payments and bills from your customer, supplier, or bank accounts that use different currencies. However, this won't change what was set up in your account. For reference, please check out this article: Set up and use Multicurrency in QuickBooks Online.

Here's a resource to learn more about how QuickBooks uses exchange rates: Learn about exchange rates in QuickBooks Online.

Feel free to reach out if you have any questions or concerns about handling your currency in QBO.