If the performance deteriorated over time, may be the CPU bending slightly. Had similar issue with the 12700K. A slow process, but after few weeks noticeable.
I suggest the Thermalright contact frame and some thicker thermalpaste (Gelid GC Extreme or Arctic MX6). It's relatively cheap, just don't overtighten, as it may cause issues. As modern CPUs boost as high as possible, and normally run hotter than ever, I found that the Thermal Grizzly Kryonaut doesn't last as long, as constant 80-85C would cause pump out.
For air, I would suggest Thermalright, again, as they're absolutely great, despite their 35-40 pounds price. Phantom Spirit Evo looks great, with very subtle ARGB.
Note that not every cooler would necessarily perform as good, or as bad, on AMD and Intel. Hardware Canucks done some interesting testing.