Without accounting for level of technical aptitude, and assuming one seeks security as in security from corporate or dragnet state surveillance, there may be a few hardware options out there.
Assemble a workstation using boards flashed with (mostly) liberated firmware, or preassembled from a company that will do it for you.
System76 purportedly uses their own spin of the somewhat-free firmware above in their more modern desktops.
Or sidestep the issue of x86 insecurity and backdoors by pursuing something like Raptor’s Power9 workstations, either preassembled or build it yourself. Or with SiFive’s Unmatched boards, which use RISC-V CPUs.
The folks at Pine64 seem to be doing some good work with ARM based laptops. Although I’m not so familiar with these.
I place so much emphasis on trusted or open hardware and firmware because these things form the foundation of any system and if either cannot be trusted or owner-controlled then it doesn’t much matter what software is installed on top of them. Many newer computers have literal backdoor hardware rootkits embedded which I regularly point out in online discussions, since that is the type of hardware that will enable the new globalist order to build their panopticon internet.
To anyone who might have found the options overwhelming, I would like to simplify things through the power of analogy. How might these look in the context of aviation?