There are some Roku TVs that have successfully used a USB Ethernet adapter, but I can't say what TV and what adapter worked. You might do a search of the Community here and see if you can find an older post. They aren't officially supported, but they have worked.
For Roku players (not a TV version), no Ethernet adapter is available. The Ultra has an Ethernet jack if you must have a wired connection, but you can't add one to devices without them.
Dan
Roku Community Streaming Expert
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