I am using a Samsung 10" Tablet and the app starts in Portrait mode instead of Landscape mode. TheStartup videos play ok and are correctly oriented. How can I turn the startup screen to Landscape also?
You cant - its programmed that way.
You'll need to contact Roku directly to give them feedback about changing that:
chat or email: https://support.roku.com/contactus/contact-options (choose setup/ultra/other/need more help?)
Have you tried one of the apps that forces other apps to display in landscape?
You may have to use the force app Everytime you restart the device.