[Lenovo Legion Y700] bloomfielderic:
Very nice to see Y700 get it's own place on XDA! I myself had just bought the 12GB version and have been very satisfied. The tutorials and info related to this model had been very difficult to come by and mostly in other languages, so I had to do my own research and exploration. So far I was able to flash ROM and extract it's boot image for root thanks to the following tutorial (in Japanese)

boot.imgを入手できない機種でMagiskを導入する方法【DSU Loader】

Android端末のカスタマイズやRoot権限の使用が可能となる「Magisk」ですが、一部例外を除き、導入に…

smartasw.com

The boot image extraction part is trickier as Y700's roms come in GSI form. But with a workaround we can still achieve the same goal. (I heard that you can also use QFIL to do that but I haven't been able to make the tool work, so if someone else can make a tutorial that'd be great)

First you need to prepare:

- DSI-Sideloader from https://github.com/VegaBobo/DSU-Sideloader/releases

- Magisk Manager from topjohnwu's GitHub repo

- a GSI ROM with built in root permission. The one the tutorial was using: https://github.com/phhusson/treble_experimentations/releases/tag/v402 --> go download "system-squeak-arm64-ab-vanilla.img.xz" (~600MB, smallest needed to fulfill the task)

- turn on developer mode and ADB debugging. Get Google SDK platform tools ready and USB drivers installed.

Connect your Y700 to a computer. Check if ADB works.

Next, install the DSI-Sideloader app. Also extract the .xz package you downloaded above to get the .img image (should be ~1.7GB in size)

Copy the image to your Y700 tablet. Open the DSI-Sideloader app, load the image, set userdata size to default (2GB). You can leave image size unchanged.

NOTE: if you have an SD card inserted, click on "config" and check "Unmount SD", or just eject your SD card from tray. Failing to do so will result in error in the install step.

After you're done, click "Install". Once finished there will be a pop-up with commands you need to enter in the terminal of your choosing. On your computer navigate to the directory containing executables of Google SDK platform tools, fire up terminal, enter the 1st command (says non-root) as instructed, and run it.

You will see a progress bar in the drop-down notification area which will complete in a moment and prompt you to reboot. Do that from there.

After reboot you will be running the modded Project Treble ROM, with root access. It's a full fledge OS but once you shutdown / reboot you will go back to your own OS. Treat it as a LiveCD of some sort.

While still connected, turn on dev mode + ADB debugging and go back to terminal for some ADB work. Next we will be extracting boot image under the current environment, made possible by it's built-in root permission.

Run the following line by line:

adb shell

su

cd /dev/block/bootdevice/by-name/

mkdir /sdcard/backup_img

for file in *; do
if [[ "${file}" = boot* ]]; then dd if=/dev/block/bootdevice/by-name/"${file}" of=/sdcard/backup_img/"${file}".img ; else continue ; fi
done

The 4th command creates a new directory storing extracted boot image, in our case /SD card/backup_img; and the 5th command is the meat of the entire process. It consists of 3 lines, key in one at a time and press "Enter". First line is "for...do", second is "if [[..." to "fi", third is just "done".

After some time the extracted boot image will be stored under the directory specified by the 4th command, in our case /sdcard/backup_img . They are stored in the temporary user space and once you reboot to your original OS you won't be able to access them again. So you need to turn on File Transfer mode, go to the actual directory on your PC and move them to your computer. They have the filenames "boot_a.img" and "boot_b.img" . After you're done, just reboot as usual and you'll get into your old OS.

Now you have the boot images, all that's left is to use Magisk Manager to patch them, enter fastboot mode, and flash the patched images using the following commands:

fastboot flash boot_a patched_img_A.img

fastboot flash boot_b patched_img_B.img

(Rename as needed)

And now your Y700 is rooted.

The linked Japanese webpage also talks about working Android 12 / 13 GSI flavors, patches, and ways to set up your Y700.