Nice to have you here in the Community. I'm here with some insight to provide on your question regarding changing the tabs on the toolbar.
I can see how adding a personal touch to the toolbar can help you easily navigate through QuickBooks. While we don't have this option, I'm going to submit a feature request on my side, which is sent to the Product Development Team for review.
They're constantly looking for great ideas from users, like yourself, when deciding how to enhance QuickBooks Online.
Keep in touch if there's anything else I can do for you, in the meantime. I'm always here to provide help and answer any questions that you may have. Wishing you a lovely day!
You mentioned looking for ideas: I'd like to have default tabs in the desktop app. What works well for my business is to have the tabs "Clients", "Invoice," and "Payment" always open. I know there are other workflow options, but this works well for me. So to have the option that these three tabs are automatically opened on startup, would prevent me from having to navigate to the selection I need, open another tab and navigate, open a third and navigate. If default tabs were an option, users could select whatever works for their workflow. Thanks.