That cooler should be sufficient. See video to check if you've installed it correctly.
View: https://youtu.be/2xCa9_zEq7s?si=cTdDgW83w0jFocyL
Use Core Temp to check cpu temp. I think what you're seeing is correct and cpu probably throttling to slower speeds when you see temps drop while gaming.
What case have you got and does it have intake and exhaust fans? And how are they configured?
Strange CPU temperature, CPU doesn't cool
I immediately noticed that on the desktop the CPU was about 80 degrees (Celsius). Instead, while I was playing it went down to 45 degrees. I warn you that I have already disassembled the heatsink and changed the thermal paste, the heatsink is well fixed to the processor, the fans are connected to CPU_FAN, the fan curve is set perfectly. There is a good airflow in the case. I then tried to lower the CPU voltage from the standard 1.380 to 0.9 and the temperature remained fixed from 40 to 50 degrees both in idle and in game. Did I do well to lower the voltage? What could be another solution? What is the correct voltage? Thanks to everyone.
CPU: Ryzen 7 5800x
MDB: MSI B550 Gaming Plus
RAM: Corsair vengeance 2x8GB 3600Mhz
PSU: NZXT c750 80 plus gold
CPU COOLER: Arctic freezer 36
GPU: Asus Nvidia rtx 4060 OC