[snvzz]

>So, it is not a meaningful to ask if the RTOS has been certified in some way to always meet deadlines.

It is meaningful. If the system doesn't offer these guarantees, no matter how good you are and how much effort you put into what's within your scope to implement, you won't be able to offer any guarantees.

This is ok if you can afford to fail. Just don't use it e.g. where human lives would be put at risk.