There is no such function on a Roku device. While the TV itself will likely remember the last used input was an HDMI port, the Roku can only power on to the Roku home screen. If you leave the Roku powered on you can usually leave a particular channel open (such as Spectrum TV), but remember that if it's streaming when you turn the TV off it will continue streaming and using your data.
I don't have Spectrum, but from what I've heard there's no ability to configure a default channel to be selected when the channel is opened.
Dan
Roku Community Streaming Expert
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