I'm giving up on this. I have tried everything and I can't make it work, so bye bye GPU.

I really want try it but I had a few difficult days... I hope I can try this tomorrow

Not sure how to change the driver to AMDGPU, I blacklisted the Radeon driver but the kernel didn't load the other one. I read somewhere that I have to do a initframs update but the command doens't exist in truenas scale. How do I force to load the other driver?

Thanks for the answer.

Just checked with lspci -v and it says radeon:

03:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Cape Verde PRO [Radeon HD 7750/8740 / R7 250E] (prog-if 00 [VGA controller])
        Subsystem: PC Partner Limited / Sapphire Technology Cape Verde PRO [Radeon HD 7750/8740 / R7 250E]
        Flags: bus master, fast devsel, latency 0, IRQ 28, NUMA node 0
        Memory at d0000000 (64-bit, prefetchable) [size=256M]
        Memory at fbf80000 (64-bit, non-prefetchable) [size=256K]
        I/O ports at e000 [size=256]
        Expansion ROM at 000c0000 [disabled] [size=128K]
        Capabilities: [48] Vendor Specific Information: Len=08 <?>
        Capabilities: [50] Power Management version 3
        Capabilities: [58] Express Legacy Endpoint, MSI 00
        Capabilities: [a0] MSI: Enable+ Count=1/1 Maskable- 64bit+
        Capabilities: [100] Vendor Specific Information: ID=0001 Rev=1 Len=010 <?>
        Capabilities: [150] Advanced Error Reporting
        Capabilities: [270] Secondary PCI Express
        Kernel driver in use: radeon
        Kernel modules: radeon, amdgpu

Is that the one it's supposed to be active?

About the allocate thing, I think that is a number and not an index in an array. I think that you can allocate as many gpus you want:

I've seen that same menu in screenshots and I'm supposed to be able to choose something different from zero.