The 3.5 update fixed the problem with the bootloader.
Code:
Model: Poke5P
Finger: Onyx/Poke5P/Poke5P:11/2023-11-17_05-41_3.5_801526b7d/6777:user/dev-keys
Link: http://firmware-us-volc.boox.com/9ba08e866b3617763dadb55a2ccda422/update.upx
Size: 1600986982
MD5: 9ba08e866b3617763dadb55a2ccda422
The Poke5 is not Secure Boot.
The QCS2290 in the Poke5 seems to be part of the SDM662 family which is used in other Onyx (and for which we have Firehose loaders).
The problem
seems to be that the QCS2290 uses a special PMIC, the PM4125.
Apparently none of the Firehose loaders in the wild support this.
That's why the SDM662 Firehose loader loads happily but the Poke5 reboots.