I made a mistake here in in using the word sentient the way I did. To help you understand here, I use these words as follows.
Sentient - to be aware of yourself.
Sapient - to be humanlike in your ability to think and speak
Conscious - to have a self experience of any form.
What I am saying is that an LLM is definitely not aware of itself. It doesn't receive itself as an input, so it cannot have thoughts like "I'm happy right now". It's functionally incapable of doing so because it has to receive itself as an input in order to do that.
However, it's possible that such a machine still has a experience of some form in the sense that there is some ethereal consciousness created by the fact that exists and is thinking, but we can't observe that aspect of the world so it's not really something we can discuss in a functional way beyond speculation.