Intel

I saw almost a constant 7deg change with a contact frame on my 13900k in an SFF build. For $12 or whatever it costs, may as well just include it.

As the chip heats and cools over lifetime it will expand and contract slightly. The Intel sockets are characteristically more rectangular and the point of contact from the default bracket extends across the longer sides. This has been a thing since LGA1200 with the amount of volts and level of turbo boosting to compete with competition. The benefit of LGA1700 is that there are 4 through holes for the CPU retention bracket, versus only 3 on LGA1200. With a third party ILM bracket you can more evenly distribute the pressure and lessen the bowing over time.

I would also recommend lowering the max clock below what the chip is designed for. CPUs have come a long way. My Asus board lets me create profiles, so i have one preset with turbo disabled and one with a -1GHz debuff. Max temps under water are 42/56 respectively, after my last LGA1200 died after 18 months never exceeding 75*C. If not going water, look into good air cooling reviews. I'm a huge fan of Noctua for a balance of performance and acoustics.

What kind of cooler do you have? Many coolers are convex, so adding washers/contact plate can mean less contact (Although this may not mean it's making it worse since the important part of the cooler and IHS, the center, is still touching).

When people have the issue, it's generally because they're using an AIO that's completely flat, which means less contact in the middle, where all the heat is.