If you face issue of roku remote stopped controlling volume. Try these hacks:-
To reset the Roku, unplug the Roku and its power cable, wait 10 seconds, and then reconnect them. This can sometimes restore the remote's functionality, allowing you to change the volume.
Change the HDMI port: Connect the Roku to a new HDMI port. You wouldn't be able to alter the volume with the remote if the port was broken.
Change A/V port: Similarly, if your Roku relies on an external A/V system for sound, ensure that it is correctly connected and isn't having any issues.