I’ve been trying to watch movies on Roku but haven’t gotten it to work
Short answer is no … Roku is not supported.
There used to be a workaround using Plex channels … but I think Plex has discontinued their support for plug-ins / channels. https://forums.plex.tv/t/new-roku-update-has-no-plugin-support-at-all/342436
Maybe you can get better help in the subreddit? https://www.reddit.com/r/Roku/