(i use unity)
I change the Time.TimeScale to something below 1, then set a bool to true whenever time is slowed,
then on the player controller i created a float that changes between Time.deltaTime and Time.unscaledDeltaTime, so whenever the bool is set to true the float will change to Time.unscaledDeltaTime,
and if you're using rb.addforce, inside the function i just divide it with Time.TimeScale
that's all i did, i hope this helps you!