This is the option: hardware.system76.power-daemon.enable
You probably want to include the system76 nixos-hardware module instead, though, in case additional settings are required in the future and added upstream, so you don’t have to think about that manually: https://github.com/NixOS/nixos-hardware/blob/9d87bc030a0bf3f00e953dbf095a7d8e852dab6b/system76/default.nix
Also see about adding the device-specific modules in the system76 directory, in case there’s one for your specific device.
That said, GNOME 40+ setups will cause the daemon to fail even if you configure this. I’ll see about submitting a PR to fix that at some point, likely forcibly disabling the GNOME power daemon if the system-76 one is enabled. I can’t test it though, so feel free to submit your own 
As for @curriedFunctions, could you share your configuration as well?
Given things work on the other thread, would be nice if you could try NixOS stable as well, just in case this is a regression. Makes it easier to track down the problem.
An lsmod and dmesg would be nice too, your logs indicate kernel issues.