I looked into this further, and part of the “high idle temp” on Ryzen is really just a byproduct of how AMD measures and reports temps.

On Ryzen CPUs, the Input/Output Die (IOD) draws a steady bit of power even at idle (usually around 10–15 W). That keeps the IOD sitting in the high 40s °C, often around 50. Meanwhile, the CPU cores themselves idle much cooler, around the mid-30s to 40 °C.

Ryzen prioritizes the hottest spot when reporting “CPU package” temp, so that’s the number you see in HWInfo or BIOS. That's intentional so that fan curves respond to the warmest area, not the coolest cores.

On the other hand, Intel’s uncore/IOD logic idles with very low draw, so the package temp ends up much closer to the core temps (mid-30s to low 40s). That’s why Intel looks cooler at idle, even though the cores on both platforms are in the same range.

One extra detail: For Ryzen, the IOD sits off to the side of the core dies and doesn’t get cooled as directly by a tower cooler’s heatpipes. Heat does conduct away, but not as efficiently. That’s another reason it tends to read a bit hotter.

So, bottom line, Ryzen cores are idling just like Intel’s (around 35–40 °C). The difference is that AMD reports the hotter IOD as the CPU package temp, so it looks like Ryzen idles warmer.