Now car won't start and engine light is on?

This is not a common problem enough to know one specific thing to tell you however, it is a pretty common issue on a lot of vehicles so let's start from the beginning.

If the check engine light is on, let's check the codes and find out what is there.

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

Also, where are you finding the mold in the car? Clearly that points to a corrosion issue and water in a module like the BCM would help explain all this.

Based on what you are seeing, this would make sense that the BCM has water in it as it is on the passenger side floor but clearly we need to get a little more info on this.

See below for the BCM location for you to pull the carpet back and check. Let us know what codes are there and what you find with this and we can go from there. Thanks