I knew I had seen this feature a while ago. Here is the Addon which made it possible back then:
https://www.wowinterface.com/downloa...Fade.html#info
Sadly it is broken. Error:
Message: Interface\AddOns\daftFrameFade\daftFrameFade.lua:10: Attempt to register unknown event "UNIT_HEALTH_FREQUENT"
Time: Sat Oct 1 00:51:36 2022
Count: 1
Stack: Interface\AddOns\daftFrameFade\daftFrameFade.lua:10: Attempt to register unknown event "UNIT_HEALTH_FREQUENT"
[string "=[C]"]: in function `RegisterUnitEvent'
[string "@Interface\AddOns\daftFrameFade\daftFrameFade.lua"]:10: in main chunk
Locals: (*temporary) = <unnamed> {
0 = <userdata>
}
(*temporary) = "UNIT_HEALTH_FREQUENT"