Update: seems fixed on Linux kernel 6.0.9 / 6.1, commit 1598bfa “platform/x86: hp_wmi: Fix rfkill causing soft blocked wifi”
TL;DR The temporary fix is either blacklist the kernel module hp_wmi currently, or comment out codes that provides rfkill function in that module.
Recently Windows auto-updated the BIOS of my laptop HP Elitebook 865 G9 to (U82) 01.02.01 Rev.A,
then in Linux the wifi and bluetooth device keeps on and off, seems 1-2 time(s) per second,
and character ^@ of unknown source keeps being inputed, even in emergency mode
(which make it almost impossible to type in password for root, thus cannot access root shell.)
I tried to boot into different kernels and found that both 5.19.x and 5.17.0.1016.15 (current linux-oem-22.04a) have this problem, but 5.15.0.47.47 (linux-generic of Ubuntu 22.04) not.
I even bought an Intel AX210 to replace the Qualcomm Fastconnect 6900 inside, but still nothing changes.
Today I occasionally disabled the hp_wmi kernel module,
and the icon of network does not flicker anymore!
I found an update of hp_wmi during 5.15 and 5.17 and tried to debug that, but no luck.
However commenting out codes about rfkill in hp_wmi does help,
so maybe some changes of rfkill and/or the userspace process and/or whatever else
are incompatible with current version of BIOS.
The temporary fix is either blacklist the kernel module hp_wmi currently, or comment out codes that provides rfkill function in that module.