How does rooting affect full disk encryption (Oneplus 3T)? My oneplus 3T running Oxygen OS 9.0.6 (Android 9) came with full system encryption by default.

I want to install root but also keep full system encryption.


Will root disable encryption?
Does root allow to bypass encryption / lock screen with adb or some other method? (I. e. in any case)
I am familiar with the half-baked Android system backup feature. is there a way to root the phone without a factory reset? if not, what is the best way to create a system image or similar so I don't have re-install and configure  everything over again?
what is the difference between system and systemless root?
no, rooting does not affect encryption   
encryption remains safe. depending on user (who is responsible for granting root access) it is not vulnerable as long as malicious app has no root permissions  
rooting does no factory reset. once rooted, the simplest straight forward backup method is (FDE)
adb pull /dev/block/dm-0  
rooting system is outdated. systemless root does it's stuff without modifying system (to preserve functionality)  


However, the answer becomes invalid when we are talking about unlocked bootloader  


attacker can flash modified boot or recovery  
TWRP may able to decrypt userdata partition without asking for credentials when FDE uses default_password (which seems the case for you)  
attacker can inject scripts without having access to encrypted userdata, which can wait for the user unlocks it's device and then gain access to decrypted userdata. for FBE it is possible to modify credentials (not the case for you)  
unlocking bootloader requires factory reset. your only chance for full backup would be a rooting method without unlocking bootloader, which is afaik only available for Mediatek devices and for the Galaxy S9 and Note 9. you rely on common (non-root) backup solutions