After using LineageOS for long time, I have finally moved to GrapheneOS. I use a lot of banking and financial apps which I never felt comfortable using on LineageOS due to lack of proper sandboxing, unlocked bootloader etc.
GrapheneOS works flawlessly just like Android. You don’t even notice there’s hardening underneath. Also it protects from Google’s evil location tracking using WiFi/Bluetooth or even when the Location is turned off. I don’t understand how people in general are comfortable with Google tracking all the time. You can use Google Play and Play Services in a sandbox that works just like regular installation, but without deep tracking.
If you haven’t tried GrapheneOS, try it. You won’t go back to regular Android.
You can make changes to the OS when it isn’t booted. You can even compile your own image. The problem is having root in the application layer. You are exposing yourself to unnecessary risk. Ideally you should flash a overlay in the Lineage OS recovery or TWRP. You can do this for a few other things such as the F-droid privileged extension.