To my knowledge there's no app/channel that is designed solely to watch local OTA stations. There are a handful of channels that might offer the major networks, but they won't have the sub-channels available. And of course there's no tuner in any Roku player, so you can't just hook up an OTA antenna to a Roku player.
But, there are ways to access OTA local stations with a Roku. It requires a networked OTA tuner on your home network. One company making these tuners is Silicon Dust. I have their HD Home Run Flex 4K unit, which provides four tuners (two that support ATSC 3.0). SD offers a channel for Roku devices, but Plex is also capable of connecting to the network tuner and allows access to whatever it receives.
Remember that Plex requires a server component running on your network, either on a PC or a NAS device. The server is what connects to the network tuner and provides the stream to the Roku. If you're away from home, you can connect to Plex to watch any of your local media, but the network tuner is not available when you are off your local network.
Dan
Roku Community Streaming Expert
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