[Croat]

Thanks for the suggestions. Here's what I tried and found:
What worked:

Downloaded and flashed frp_oemunlock.img to frp partition
Flashed ablmod.img from the Palma 2 guide to abl_a/b
Erased devinfo
After reboot fastboot flashing unlock now returns OKAY — bootloader is properly unlocked

What didn't work:

Any attempt to boot an image via fastboot fails with Failed to load/authenticate boot image: Load Error
This applies to stock boot.img, stock recovery.img, and even fastboot --disable-verification makes no difference
fastboot flashing unlock_critical completes successfully but doesn't help with image authentication

Conclusion:
The ablmod from the Palma 2 guide appears to enforce signature verification using Palma 2 specific signing keys. Since the Note Air 5C uses different keys, all images are rejected. I restored stock abl_a/b from the 4.1.2 firmware but kept frp_oemunlock and erased devinfo in place.
Current state:

Bootloader unlocked (fastboot confirms)
frp_oemunlock flashed
devinfo erased
Stock abl restored
Still stuck on Boox logo

What I've done overall via EDL (full summary):

Complete partition dump saved before any changes
Compared all dumped partitions to stock 4.1.2 — found abl, aop, dtbo, xbl, modem, vbmeta were all modified
Flashed stock versions of all modified partitions
Built and flashed clean super.img from extracted 4.1.2 partitions using lpmake
Cleared misc partition (was set to boot-fastboot)

Question:
Does anyone have a Note Air 5C specific ablmod, or a full EDL partition dump from a working 4.1.2 English device they'd be willing to share? The fastboot unlock is now working so we're closer than before.