Rooting V1 - OS 2.4.52 SW 2.3.76 (procedere works on V1.5 too)
Disclaimer: I'm absolutely not responsible for anything you do, including flashing and modifying anything. It's your own risk. What I describe here is what I have done, your miles may vary.
Needed: "Open Settings" from Playstore, full ROM from cardongle.dev/community/postid/1522/, a copy of Magisk.apk from https://github.com/topjohnwu/Magisk/releases/tag/v25.2 (the latest), Mirroid or Vysor on the PC, driverset from https://androidmtk.com/download-mtk-driver-auto-installer, Minimal ADB and Fastboot from https://androidmtk.com/download-minimal-adb-and-fastboot-tool
Install Mirroid or Vysor (my favorite) to your PC, extract Minimal ADB to a new folder on PC, extract the downloaded ROM to a different new folder, install MTK driver to PC. Connect Cardongle to PC, download and install Open Settings, download Magisk to SD card (internal memory will be deleted several times).
Start Open Settings on Cardongle, navigate to System -> Advanced -> About Phone -> Build number, tap 7 times on Build number and you'll be a developer. Go back one level and open Developer options. Allow OEM unlocking.
Back to PC. Navigate to the new folder ADB (I called it ADB, you might have used another name), start cmd-here (a new command windows pops up). Enter "adb devices" (without quotes), you'll get your serial number as a response. If not, the driver or ADB wasn't installed correct. Now "adb reboot bootloader" and wait for a while. then enter "fastboot devices". The same serial number should appear, if not driver install was not successful.
Following is the unlock part: Enter "fastboot flashing unlock", wait 5 sec or more after enter, then "fastboot flashing unlock_critical", 5 sec wait, then "fastboot reboot". The device now is unlocked.
Now you might grab a coffee or smoke some cigarettes because you have to be patient for at least 3 minutes. and another 5 minutes (for the automatic optimization process). Cardongle will connect and reconnect several times, before it reboots successfully - be patient. To finish the process disconnect and reconnect Cardongle (to reinitialize), goto Cardongle Settings and establish mobile hotspot again, open Playstore and install Open Settings again. Check System -> Advanced -> Developer options. The option OEM unlocking is greyed out and tells you "is already unlocked".
Next step install Magisk on Cardongle and copy the boot.img from the downloaded ROM (on your PC) to download folder on Cardongle. Open Magisk and click on install Magisk. Allow all permissions, click next, choose select and path, change to download folder and choose boot.img, then click LET'S GO. A new file will be created in download, copy this file back to the ADB folder on your PC. Rename the new copied file to bootm-V1.img (or any other name except boot.img)
Back on PC open cmd-here in ADB folder and enter "adb devices" in the new window. All's well if you see your serial number again. "adb reboot bootloader", short wait, "fastboot devices", short wait, "fastboot --disable-verity --disable-verification flash boot bootm-V1.img", short wait, "fastboot reboot", done. As usual it's time to wait again to re-establish the connection to Cardongle (maybe you have to disconnect/reconnect Cardongle to get it booting). No matter, be patient!
Patience is the key for successful modifying your Cardongle (can't say it too often). If you have any questions you can ask, I might or might not answer :-). Depends on my mood and on the kind of the question. This procedure is checked and tested several times and it will work for anybody who wants to understand.
Bye for now Fred