Most current generation Roku streaming players and Roku TVs support screen mirroring with notable exceptions listed below. To find the model of your Roku device, go to Settings > System > About.
Roku Express: Screen mirroring is only supported on model 3900 (introduced in 2017), and not on model 3700.
Roku Express+: Screen mirroring is only supported on model 3910 (introduced in 2017), and not on model 3710. With model 3910, screen mirroring is only supported on the HDMI output, and not on the composite, or A/V output.
StreamerUser Roku Community Streaming Expert
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