The gray oval with -0.79 inside and the yellow oval with 5.21 in it is what I'm talking about.
All Fabfilter plugins contain a similar level monitor.
From what I can tell, FL lacks this incredibly useful workflow feature. The meter on the mixer does not accurately display the level, meaning you have to guess the dB value of whatever you're inputting into a mixer track. You also have to diligently pay attention to dynamic inputs that tend to have random jumps in volume. For example, if I have a recording of a live drummer, and I'm trying to gain stage, then I will have to listen to every second of the audio clip while paying close attention to the meter to make sure I can be accurate. Having an actual value display that can track the highest dB level would allow you to do something else while you let it capture the highest peak level.