You can remove the thermal throttling "BlackBerry Launcher" and replace it with a third-party launcher like Nova . You can disable the DTEK services that constantly poll the CPU.
If you already own a Priv: Keep it in a drawer. Take it out occasionally to slide the keyboard and feel the nostalgia. But as a daily driver with a custom ROM? That ship sailed in 2018. The BlackBerry Priv represents a "what if" moment in mobile history. It is a tragic hero of engineering. While the custom ROM scene for this device is effectively dead , the spirit of tinkering is not. Blackberry Priv Custom Rom
You will find XDA threads from 2016-2018 with titles like "[WIP] CyanogenMod 13" or "[Alpha] LineageOS 14.1." These projects were abandoned years ago. You can remove the thermal throttling "BlackBerry Launcher"