Hey, I have the same device and just updated to 8.2.2 Developer image but lost root.
How do I install Magisk 23 on this? Should I patch the boot.img on another device and flashboot flash it to the Shield TV?
I'm also interested in installing TWRP as well (I had it before updating) but I can't find an up-to-date guide anywhere.
As long as your bootloader is unlocked, it really is as simple as patching the boot and flashing it to the device.
If recovery is still a separate partition (newer partition layouts moved it into the boot image), that is just like flashing a boot image using "recovery" instead of "boot" as the target.