Edit: Removed non necessary writings, started over after refashed stock ( before flashing stock I had following at fastboot / bootloader: errors 11 (recovery image) and 2 (load failed). )
Allright, I took my old Honor 8 from drawer, its bootloader is unlocked and it was running openkirin version of LineageOS 16.0, before reflashed to stock and...
To install TWRP to this device:
fastboot flash recovery_ramdisk FRD_TWRP_S_mak_KV_v2_EMUI8.img
Sending 'recovery_ramdisk' (24258 KB) OKAY [ 0.665s]
Writing 'recovery_ramdisk' OKAY [ 0.171s]
Finished. Total time: 0.866s
And to start twrp cable needs to be plugged off, then power + volume up to get into twrp.
fastboot reboot recovery
Rebooting into recovery OKAY [ 0.021s]
Finished. Total time: 0.072s
Now my only problem is I would need newer twrp compatible with Honor 8 frd emui 8. twrp should support adb so I could do some last fixes to get CAOS A11 GSI to boot. It does boot on first time, but after reboot requires needs to format data. To fix this will lead to situation which could be fixed through adb.