you only need to unlock bootloader once, unless you relock back your bootloader, then you have to unlock again
things you need
twrp, decrypt.zip and the firmware
oh yeah you need to edit something inside firmware file zip... here https://forum.xda-developers.com/showpost.php?p=78667159&postcount=29
you will lose your data!
wipe data, system, cache, dalvik
install>flash the firmware
reboot to system
@watatara.102, I have some how managed to rectify that bug report generation on v186. I had to install v179 and v186 for 2-3 times for different reasons, and now v186 is working fine without that bug report generation on reboot. I have installed xposed SDK27 v90b3 and xposed is also working fine, earlier my camera was not working on v90b3, but now camera is also working fine with xposed. I don't know why, my banking apps were not working (when xposed was not installed) even after hiding root from them in Magisk, so I can use xposed as well.