The brand of appsheet when opening a url within the same app can be changed by another name ?, is for a public application.
I don’t believe that’s configurable (@Gil can probably confirm). As a workaround, you could enable the Launch External property of your URL column or Action definition. That will make your app open the link in the external browser on the device (instead of within the AppSheet container app).
White labeled apps will display the app’s name instead of AppSheet in this back button.
On iOS, even if you open the link in an external browser, there will still be a small back button with the AppSheet text.
This is not the case on Android, because there is no on screen back button.