Ok, so apparently the problem comes from the kernel module pinctrl_amd.
I’ve blacklisted it by adding this to /etc/modprobe.d/blacklist.conf:
blacklist pinctrl_amd
This fixes the issue, but it also breaks the power button and the touchpad so it’s not a solution for me.
I will wait for an update. In the meantime, if I want to lower the temperature, I can set the governor to powersave during charging or disable CPU boost.
There’s also the possibility that this is a HW issue from the charging controller or noise on some IO interrupt pin, but since I did not see this problem in Windows, I hope it’s not.