I stumbled into this problem while trying to install BusyBox. I have a OnePlus 7 pro with LineageOS 16 (rooted). But the solution might work for other devices as well.
- enable ADB root access on your phone
- connect phone to your computer
- type the following into your cmd window
adb root adb disable-verity adb remount
- install BusyBox to e.g. /system/xbin
- (optional) revert changes
adb enable-verity adb remount