I'll elaborate on some details on this, Tredici.
For now, filtering on the invoices window on the left side is unavailable in QuickBooks Desktop for Mac. As a workaround, you can run a report for your customers where you can filter or sort classes. The report I've added below may be an expense report however it works the same when sorting classes. You'll only have to ensure to pull up customer reports for your invoices to show up.
Streamline your finances and take control of your business with ease. Our easy-to-follow guide will help you navigate every feature, from invoicing and make the most of your accounting task. Discover the power of QuickBooks Desktop for Mac with this comprehensive manual: QuickBooks Desktop for Mac Manual.
Furthermore. learn how you can create and manage reports. I've added these articles for reference: Create and Manage Reports.
You can always get back to us if you have any questions about classes or invoices. I'd be happy to help.