As far as the version of HDMI on a Roku device, Roku doesn't show it within their hardware documentation on their web site. The Wiki entry for Roku shows the 4K players all have HDMI 2.0b, with the exception of the Streambar (9102R) showing as HDMI 2.0a.
If you're referring to a Roku Ultra, it should have HDMI 2.0b. That said, it will of course work just fine in an HDMI 1.4 connection, only it won't offer 4K/60 resolution or HDR support.
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