Thankyou so much.I'm currently on Oxygen OS 9.0.9. I'm not a new custom rom User but still please help me with these queries:-
-Do i need to decrypted/encrypted to flash this ROM?
-Which twrp would you recommend? Official or any other name please?
-Any custom kernel for good battery backup?
-Do i need to flash any firmware?
1. Yes, make a backup of your data and go to wipe -> Format Data, reboot to recovery, wipe -> Advanced wipe -> Data and probably Internal storage (not sure about this one). Play with those options, always reboot to recovery in between. You con't do anything wrong. When TWRP doesn't ask you for a password anymore, you're decrypted.
2. Official can't decrypt. Use codeworkx (has a thread in here) or blu_spark (on GitHub).
3. My phone can run 24h or more and that's fine for me, so I don't need one and otherwise can't help you with that.
4. I think 9.0.6 or higher. It will stop flashing and tell you which version to get if you're below the required one.