I still wanted BetaFPV because I use it to configure my drones, but this search led me to a forum where a user said in 2024 that BetaFPV does not work at all in Linux. Seems weird given they literally have a download for it, but I did find a flatpack for betaflight and hopefully that will let me configure the serial port. See my update comment.
I did find out how to create and load a new udev rule with the controller info, but still no dice on getting liftoff to detect it.