[Renate]

If you can get to fastboot you can reflash the copy of the stock boot.img you pulled off to magisk. That will give you more info on what's up. As I said, I can't put my finger on it, but when fastboot boot doesn't work, I always just flash. That goes for recovery too. Since your Nova doesn't have A/B you can flash /misc with "boot-recovery" so as to boot into recovery.

What do you have for stuff? The latest boot image? Post it and I'll try to make you a recovery.

Just to clear up why you'd want to do what:
fastboot: you can write or erase partitions, but not read them
EDL: you can read, write, erase partitions
Rooted recovery: you can read, write, erase partitions and with the right recovery you can install an update.zip

You can get to EDL from a working adb: "reboot edl".
You might be able to get there with an "EDL cable", search on ebay. (I've never gotten a cable to work.)
In drastic cases you can open your device and reset while shorting the special EDL test points. (I put a magnetic switch in my Poke3 so that I never have to open it again.)
Going into to EDL is not dangerous, as long as you don't do anything!