So, I missed "hw.battery.chargestop" sysctl and some keys (eg. keyboard backlight) on my Asus #OpenBSD install.
I spotted new driver for Asus machines in source - "acpiwmi". But not included in default kernel build. Hmmm...
On mailing list there was additional acpiwmi patch for chargestop and some other stuff. So I took chargestop logic, patched acpiwmi driver and compiled custom kernel. Works!
#OpenBSD kernel compiles in around 3 minutes !
Linux 45 minutes. Without AMDGPU stuff.
Incredible