Thank you for reaching out to the QuickBooks Community, @arie2. I'm here to help you create an expense for your other business category.
There are two ways to create an expense. The first way is to create a check and create an expense directly. However, we'll ensure you have already created an account for your other business.
Follow these steps to create an account:
Go to Transactions and select Charts of Accounts.
Click New.
Fill up the necessary information.
Select Save and Close.
After creating the account, you can create expense transactions or write a check directly.
I have attached some articles that can help you manage your Transactions: