Subscription content wouldn’t be in your Library. The Library is for purchased Store content (buy or rent) and downloaded content. Just use the Apple TV+ tab instead.
Verify that your device is internet connected. Offline devices with local disk space would only have access to any downloaded content in the Library.
Verify that your Apple Vision Pro is using the same Apple Account as what your Apple TV+ subscription is linked to.
Try using the Search function of the Apple TV app.
Or try navigating to the Apple TV+ tab of the Apple TV app. Then browse through the rows of ‘Top Chart TV Shows’, or ‘All 2024’, ‘More Standout Hits’, ‘Watch Entire Seasons’, ‘All Drama Series’.
Once you have watched any segment of a show on any of your devices, its watch progress should be tracked in the Continue Watching row on the Home tab of the Apple TV app, and also in the Continue Watching row on the Apple TV+ tab of the Apple TV app.