I've seen people mention ARM TrustZone pose some similarity with Intel Management Engine, where they have concern it could weaken security or even used as backdoor.
As far as I know and I am probably wrong, they never fully supported it on the Pi. So I don't think it's much of a worry.
You also have things like the RockPro64 and others that are based on different but similar hardware.
While it's true Raspberry Pi and other affordable ARM-based SBC doesn't fully support ARM TrustZone, we don't know the exact detail which makes those people still have concern about it.
There are also a lot of industrial SBC PCs that do not have any of the IME stuff but they are far from cheap so you would probably be better off getting one of the machines that @af_newbie mentioned.
Any example of those industrial SBC?
You can also still find older boards / CPUs out there that will work, but now you are putting decade+ hardware into 24/7 production.
Or as i stated earlier, use RISC-V based device and hope software (such as Box64) can run your x86/arm software on RISC-V device.