Same boat here.
5900X, no PBO with a brand new 280mm AIO (Liquid Freezer II), I have temperature spike that goes around 85°C for a few seconds.
I thought that it was the motherboard (B550-I Strix) that had a way too agressive boosting behaviour but I changed it and same problem. Reinstalling windows, same problem.
Changing AIO, same problem.
This behaviour is only happening in D4, i have no problem on other heavy games like CB2077, Hunt Showdown ect…
Those spike are periodic? If you record temperature from HWinfo64 and plot everything on a graph you can see it clearly.