You're right to be concerned about hardware backdoors; it's a tough issue. While no solution is perfect, you can increase your security and trust.
Consider exploring open-source hardware options like the Librem 5, MNT Reform, or Fairphone.
From personal experience avoid PinePhone(not knocking the company or saying they spy but the hardware is dated AF, shit battery life, had issues out the box that bricked it til I flashed another OS, etc)
These decices use open-source hardware as well and thus aim for greater transparency in their design and components.
Pairing such hardware with a software security-focused OS like GrapheneOS adds another strong layer, hardening your device against software vulnerabilities and enhancing privacy.
Use multiple devices for different online activities to compartmentalize what you do thus making it harder for anyone from AI to governments to build profiles on you.
This multi-devicr layered approach helps. It's not just about governments; corporations engage in extensive data collection too.
They just use it to psychologically manipulate you to buy more dumn shit.
Using more auditable hardware and software gives you more control.
While it's hard to achieve absolute certainty, taking these steps is a significant improvement over using closed, black-box systems with no transparency. Every layer helps.