Finally got my old 2015-era laptop's NVIDIA Optimus card to disable under #NetBSD by following the instructions here by @bkrawczyk@fosstodon.org ! Had to change out the ACPI methods being called to the ones used by my laptop (in my case, \\_SB.PCI0.PEG0.PEGP._OFF and _ON) which I found by running a Linux live USB, blacklisting the nouveau module with modprobe.blacklist=nouveau installing the bbswitch module, reading the kernel log of the ACPI device found by it, unloading bbswitch, building and installing acpi_call, testing with that a bit, and then rebuilding the NetBSD kernel module with the new ACPI method. Also I had to compile the NetBSD kernel without Nouveau built in. I really should write this up on the NetBSD wiki or something... (Or port bbswitch properly. But that runs into the problem of my test cases being a grand sample of one.)