Hi there, John.
The option to switch to Desktop View in your QuickBooks Online Desktop app is available only for Accountant and Intuit Enterprise Suite users. To enable this feature, toggle the Desktop View option at the top of the screen.
For visual reference, please see this screenshot below:

On the other hand, if you're using the QuickBooks Online version, please know that the option to change it already unavailable. All users are being transitioned to the new interface to ensure a more streamlined and updated experience.
If you have other questions, feel free to comment them below.