Sorry to hear you're running into trouble with Trim View, I understand how confusing it can be when a feature doesn't behave as expected. I tested this on my end using Illustrator on Windows 11 version 30.2.1, and Trim View is working as intended.
Could you please confirm the exact version of Illustrator you're using along with your OS details? Also, it would really help if you could share a bit more about what's happening on your side. Is the Trim View option greyed out, or is it available but doesn't take any effect when enabled?
In the meantime, I'd recommend trying a manual preferences reset using this video and then checking the behavior again: https://adobe.ly/4bxmCl5
Let me know how it goes or if you notice any change after trying this.