You are the third User who uses a MSI AIO that has complained about their AMD Processor overheating.
These are the last 2 users using MSI AIO CPU Cooler and having issues:
https://community.amd.com/t5/processors/about-amd-threadripper-3990x-strx4-3-7-4-5-ghz-64c-128t/m-p/...
https://community.amd.com/t5/processors/water-cooled-5900x-temperatures/m-p/502463#M44939
How are you monitoring your CPU Temperature? Are you using Ryzen Master or some other monitoring software?
First check that your MSI CPU Cooler is installed correctly and has a tight and even fitting on top of the CPU processor's surface.
Make sure the fluid is circulating through the tubes by feeling for vibrations of flowing fluid.
Also the Input tube to the processor should be slightly cooler than the output tube from the CPU Cooler.
Make sure the AIO Pump is running at its recommended RPMs by looking at MSI own CPU Cooler software or other monitoring software.
Make sure you have good Air circulation inside your Computer case and that the Radiator's fan air flow is not obstructed.
That all the Radiator's fans are running at Maximum RPM when it starts getting hot.
If all the above is good then I suggest you open a MSI Support ticket to have them check your AIO CPU Cooler. If possible install a good high TDP Air Cooler to see if you still get the same temps as the AIO CPU Cooler.
If the Air CPU Cooler are lower than the problem is with your MSI AIO CPU Cooler.