How do I keep the TV power on when I turn the  Roku power off?

Thank you for posting here in the Roku community, Larryh86GT!

We see you're trying to use your regular TV while the Roku device is plugged in, and we're here to assist.

To switch back to regular TV using your TV remote, please try to select the correct input or source on the TV remote you have. This will allow you to switch between inputs or HDMI ports for the Roku and regular TV.

Please try doing this and see if it helps with what you're experiencing.

Best regards,
Jharra

Larryh86GT, Roku devices don't turn off.  The power button on the remote is strictly for the TV.  When you're finished streaming with the Roku device, return to the Roku Home Screen by exiting the app or pressing Home on your remote and then switch use your TV's remote to watch something else.