"When your application uses an Operating System (Micrium OS kernel or FreeRTOS, for example), the process of going to sleep is fully handled by the OS. The system will automatically enter the lowest possible energy mode (depending on the requirements currently set) when the OS enters idle mode (i.e. when all the tasks are pending on something, delayed or suspended). Power manager will ensure the system resumes its operations as soon as a task is resumed, posted or that its delay expires."
Take into consideration the different power modes
https://docs.silabs.com/gecko-platform/latest/service/power_manager/overview
"When your application uses an Operating System (Micrium OS kernel or FreeRTOS, for example), the process of going to sleep is fully handled by the OS. The system will automatically enter the lowest possible energy mode (depending on the requirements currently set) when the OS enters idle mode (i.e. when all the tasks are pending on something, delayed or suspended). Power manager will ensure the system resumes its operations as soon as a task is resumed, posted or that its delay expires."