Maybe helpful:
Out of the box bluetooth was not working on my Pocket Reform / RK3588 with Intel AX210. After some time I noticed, that pairing my headphones worked when holding it as close as about 10cm to the laptop - something I wouldn’t do normally.
I installed a second internal antenna in an angle of about 90 degrees to the existing one on the opposite side of the cover and connected it to the free port of the AX210. Now I can use the Bluetooth headphone without problems.
WLAN worked fine, so I think that the “hidden copper layer” I read about was not the cause.
Claus