I have 2 Roku Premiere 4k units that are around 5 years old. Recently both remotes have developed the same issue. The left arrow button requires extreme pressure to respond. This seems to be a mechanical issue and nothing configuration related. I find it interesting that BOTH units developed the same problem at around the same time. Can this be fixed?
Remote buttons do wear out. You can try taking it apart and cleaning it, but the buttons may be damaged beyond repair. Other than that, it may be time for a new remote. Any of the current remotes (other than the one specifically for Roku TVs) will work with your Roku device(s).
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I used to rejuvenate DirecTV remotes whose keys were becoming unresponsive by taking them apart and renewing the electrical conductivity of the contact points below each key on the rubber-like keypad. I used conductive paint sold to repair auto windshield painted-on defogging traces. In a pinch I could even rub a bunch of pencil lead on a piece of paper and transfer that to the contact pads.
The tricky part is getting the case apart in the first place without damaging it. You can probably find help with this on YouTube.
Or if that's too much trouble, replacement IR remotes aren't too costly.