Did you ever heard of A/B slots? The Moto G6+ uses A/B slots and does not have a partition /recovery. Of course there is a recovery but it 's merged in the boot.img. So the boot.img is able to boot into recovery and also
Your TWRP image is recovery only and isn't able to boot into system!
What will happen when flashing TWRP to partition /boot?
In that case your boot.img = twrp.img and will only boot into recovery.
How to install TWRP permanently on your device?
First of all you should have a look at https://twrp.me/motorola/motorolamotog6plus.html
TWRP provides an installation guide for every device and it´s recommended to follow these steps.
Here´s a more detailed guide:
1. In your case you have to restore the boot.img
since it got overwritten by flashing your twrp.img to /boot.
If available use a backup of /boot. Otherwise flash the stock boot.img from your current running firmware version. Firmware builds can be found here:
lolinet mirrors - powered by h5ai
(take care of your software channel, i.e. RETUS)
*** Be aware that by flashing your stock boot.img Magisk will be deinstalled from ***
your device and as a result of this you will LOOSE ROOT ACCESS!!
fastboot boot <TWRP.IMG>
3. On TWRP main screen go to
Install Recovery Ramdisk
and pick the twrp.img:
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