PEX Line Toilet Water Supply Disconnect
With a manifold system, each branch has its own valve, so it is more common to not have a valve at the point of use.  If you are more comfortable with an additional valve next to the toilet, you can certainly add a typical 1/4 push-fit shut off valve.

If for some reason the manifold doesn't have individual valves or something is wrong with them, you would simply need to turn off the main water valve to the house so you could remove that straight fitting and replace it with a valve like you would do in an older home.