Brakes are stiff and will not start

Do you have the push button start option? If so, you are required to press the brakes to start the engine. If the engine is not starting, then I suspect the brakes are hard because you have pressed them a number of times and all the assist is gone until you start the engine again.

This means we need to address the no start issue and then I assume the brake assist will return.

If this is true then we need to check for codes and clarify if the engine cranks and does not start or when you try to start it does it do nothing?

Here is a guide on how to do this so let's start here and report back this info and we can go from there. Thanks

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

https://youtu.be/dCjmRL3p4Cs