I mostly used /e/os, so no slow charging, nor battery limit (until recently). I'm still leaning toward upgrading to the FP6 (still hesitating), this phone will either become my rom testbed, or my mother phone once hers die.
I'm currently trying IodéOS (LineageOS with some tweaks), which has this in his settings.
I unfortunately don't remember that option on my stock FP4, but there are tons of battery checker app out here which would give you those infos.
Here is one : https://f-droid.org/packages/com.dijia1124.plusplusbattery