I’ve never had a remote fail. What is the failure mode? (ie: one button fails? Always the same button? Button gets stuck?)
Many third-party universal remotes include codes for Rokus and/or Roku TVs, so if you can’t find a Roku-brand remote that keeps working, that’s an option. (This works for all Rokus which work with IR – the Roku “stick” models are the exception since they have no IR receivers.)
There is also a Roku app for Android and iOS that lets you use your phone as a remote.