Install TWRP and Magisk Manager on Moto G5 Plus without rooting I would like to install Google Play Services for AR (ARCore) on my Moto G5 Plus, running Oreo 8.1 - this device is not on the official Google supported list. I believe this is possible with TWRP and Magisk Manager. I have the Android SDK, and all necessary USB drivers installed. I can load .apk's using adb.
However, I'd like to install TWRP without unlocking the bootloader or rooting the phone.
First question: is this even possible? or do I need to root the phone?

I tried to follow the instructions to install TWRP withOUT rooting, but when I try to flash the latest version of the Potter image, twrp-3.3.1-0-potter.img, I get a 'Preflash validation failed' error:

\android\Sdk\platform-tools&gt; .\fastboot.exe flash recovery twrp.img
(bootloader) is-logical:recovery: not found
Sending 'recovery' (16342 KB)                      OKAY [  0.710s]
Writing 'recovery'                                 (bootloader) Image recovery failed validation
(bootloader) Preflash validation failed
FAILED (remote: '')
fastboot: error: Command failed


According to this answer, Moto devices do not support downgrading the bootloader. However, I figured the recovery image (3.3.1-0) was the most updated, and suited for Oreo 8.1. Is there any way to check bootloader versions of the image and that on my phone?

Thanks in advance for any insight!
Answer: it is not possible without unlocking boot loader. 
Thank you to @alecxs !

Also for anyone interested, rooting has some side effects: cannot load the Netflix app due to safety net checks. Even with the magisk mod for hiding safety net flags. 
And ultimately, ARCore still doesn't work, even after I flagged the Pixel 2 "image", and installed Google play services for AR.