The minimum requirements will essentially be the same as the regular release. TrueNAS Hardware Guide | TrueNAS Documentation Hub Notably, 8 GB of RAM, 16 GB boot device, two disks for storage, and the additional requirement of a working UEFI. TrueNAS isn’t really designed to run on very low end systems, and that holds true with the Arm variant too.
Unfortunately, I’d recommend avoiding buying the Orange Pi Zero 2W for TrueNAS. I believe it uses U-Boot, so you’d need to jump through hoops to get it to boot. I wouldn’t be surprised if the wifi driver isn’t standard, requiring a USB to ethernet adapter. You’d need a USB hub to connect connect the disks.
Your best bet would be the Raspberry Pi 5 8 GB or 16 GB or the Raspberry Pi 4 Model B 8 GB. Unlike the similar other-brand-Pi options, I believe these have a working UEFI due to the Arm SystemReady certification. But be aware that nobody has confirmed whether this is compatible, so only spend the money if you’re willing to take the risk that you can’t get TrueNAS on it.