To be clear, there is a big difference between compromised hardware and hardware with security vulnerabilities, that unintentionally result from a bug. No hard- or software on earth can guarantee you, that it won’t have security vulnerabilities. I think the only thing that comes close to it is this:
However, especially with hardware, it’s close to impossible to assure that it will stay absolutely safe until it breaks and needs to be replaced.
If you are looking for hardware, that is less likely to be filled with spy crap, opposed to all this Huawei and other China crap, plus Apple spyware shit and of course anything from Microsoft and similar companies, then you probably want Open Hardware or any hardware that comes close to the spirit of open hardware:
Those are just the most prominent examples.
Another very fresh example:
You can see how easy it is to tear it down without breaking it here:
Such laptops would probably be one of the first things a normal open source and open hardware conscious consumer would think about.
However, if you want a truly secure computer, I think you would need to e.g. borrow a Russian-made computer, which they build a lot of, because they don’t trust computer parts from China and America. They build entire computers themselves, where every single piece is made in Russia, only. Even the transistors and every piece of electrical machinery is made in Russia. These are 100% Russian computers which follow the slogan “What is done Russia, stays in Russia.”.
As far as I know, these computers are however only for the government and not simply legally acquirable. You would need to work for the Russian government to be a ble to borrow a unit.
So, if you truly want the most secure hardware, without any question about privacy, security, etc. (except security vulnerabilities that can arise any time, as described above), then you need to build your own computer, from scratch.
The more you build by yourself, the safer you are.
However, since that would be extremely expensive and tedious, I would just recommend to use a small open hardware computer, whenever you need to do anything critical.