I watched the showcase and Phil kept saying that if we have game pass we can play every game shown off at the showcase right now, so can we play the demo for Halo Infinite if so how?
No, the demo is not publicly available.
He said that all the games showcased will be available at launch.
The game will get test flights through 343i’s insider program, as was already announced a long time ago
and confirmed again in the latest blog post. Do some research next time and you’ll be able to answer
your question yourself.