I got a Roku express 4k and the remote only works comically close to the reciever box, line of sight is clear and I’ve tried moving the box and remote all around it just won’t work further than 2” from the box, this device is brand new
Try using new batteries in the remote. If no go, may be a bad IR sender in remote or bad IR receiver in the device. Either one would require replacement. Either return if in return window (30 days), or request warranty replacement. (https://support.roku.com/article/208757058)
If you purchased in a store (I believe still exclusive to Walmart), and budget allows, consider replacing it with the Express 4k+ which will include a Voice (wifi) remote with the device to eliminate the IR clear line of sight requirement.
Roku Community Streaming Expert Just another Roku user... I am not a Roku employee. Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102