Some quick thoughts:
- The icon doesn't really remind me of PRs. It looks more like a HTML tag. I would use the PR icon provided by GitHub.
- Don't show "Last updated 2 minutes ago". Just constantly update. Maybe every 20 seconds and then automatically update.
- You're not adhering to the API rate limits, so I got an error "Error: You have triggered an abuse detection mechanism. Please wait a few minutes before you try again.".
- The "Update token" should be in a settings view, not in the main view.
- The UI could use some tweaking for spacing and alignments. It's a little bit inconsistent. For example, the tab badges.
- The mute buttons are too big and take too much of my attention.