Missing "Manage root accesses" under developer options in LineageOS 16

My phone is Xiaomi Mi 5s Plus 6GB/128GB. After a clean installation (flashed MIUI 9.6.27 first) of official LineageOS 16.0 Sep 19, 2019, I can't find "Manage root accesses" under developer options.

After the format and advanced wipe, I installed LineageOS, Open GApps Pico ARM64 for Android 9.0, and Magisk 19.4. Now all three seem to be working ok, and I was able to grant root access to AdAway and Titanium backup through Magisk. But I couldn't find manage root accesses under developers options.

So I installed addonsu-16.0-arm64-signed.zip from this LineageOS page, through TWRP. Though after a reboot, the manage root accesses option is still missing. It's not even displayed as a greyed-out option, it's just not there. On the "Trust" screen, it says, Root access: Disabled right below SELinux: Enforcing.

I would like to grant root access to ADB. Is it possible through a terminal emulator (on the phone)? Is there any command for it... 'coz I can become root "by su" in the terminal emulator through Magisk.

• Official LineageOS 16 ROM doesn't come with "Addon-SU" pre-built. Their installation instructions say to install Addon-SU (separately) from the "extras" page I have linked.
• With Magisk, I know I can grant root access to any regular app but how could I grant "Root access to ADB"?

The reason I'd like root access to ADB is, 2 days ago I tried updating LineageOS ROM through TWRP but it failed, and then I couldn't flash new or old Lineage ROM through ADB, as I kept getting this error:

adb: sideload connection failed: insufficient permissions for device: user in plugdev group; are your udev rules wrong?

Even though I was running this adb sideload lineage-16.0-20190719-nightly-natrium-signed.zip command as ROOT user from Ubuntu 19.04. I also tried the same from Windows 10 admin command prompt.

So after a failed LineageOS update:

1. I couldn't flash new/old Lineage ROM through TWRP,
2. I couldn't flash any Lineage ROM through ADB.

I had to install MIUI 10 ROM, then format and advanced wipe to install LineageOS back again. So now I'm trying to grant root access to ADB to prevent this from happening again.

1. As I have mentioned earlier, I tried the same through Windows 10 administrator command prompt too, and the result was the same.

   As per my understanding, Window 10 does not have "udev rules".

2. This is how I was running adb sideload command from Ubuntu MATE 19.04 Terminal:

   admn@um:~$ sudo su[sudo] password for admn: root@um:/home/admn# adb sideload lineage-16.0-20190719-nightly-natrium-signed.zip

   Was getting an "insufficient permissions" error.

3. Here is the "insufficient permissions" error in full detail, where you can see it refers to Android developer website:

   root@um:/home/admn/Downloads# adb sideload lineage-16.0-20190919-nightly-natrium-signed.zipadb: sideload connection failed: insufficient permissions for device: user in plugdev group; are your udev rules wrong?See [http://developer.android.com/tools/device.html] for more informationadb: trying pre-KitKat sideload method...adb: pre-KitKat sideload connection failed: insufficient permissions for device: user in plugdev group; are your udev rules wrong?See [http://developer.android.com/tools/device.html] for more informationroot@um:/home/admn/Downloads#

4. Right on the phone, through TWRP: Now I have updated the same phone for the past two+ years in exact same manner. Almost once a week for two+ years.

   Note: Every single time, I always verify sha256sum before transferring the ROM to the phone.

   First I transfer the LineageOS ROM into the Download folder of the phone through a USB cable, boot into TWRP > install > find the LineageOS zip.

   But this time, first time in two+ years, the update failed with "Error 7".

   1. I tried this route many times, after quite a few reboots, but the installation was not going through.

   2. Now the phone was not booting up normally. It was getting stuck at the LineageOS logo screen for 30+ minutes.

5. I'm trying to get to this "Manage root accesses" screen:

   Of course, this image is not mine but it's from LineageOS.

6. LineageOS's "AddonSU" is NOT just meant only for userdebug builds. Here's a link to LineageOS installation instructions pages for Natrium (Mi 5s Plus) and Beryllium (Poco F1). Where at the end of a page it says: "(Optional): Root your device by installing LineageOS’ AddonSU, (use the arm64 package) or by using any other method you prefer."

   I'm attaching a screenshot: