“Skipped the docker bit”? I’m assuming you mean by using the proxmox helper scripts? If so, the path to the config file is there as well. If you are setting this all up on your own without the helper script, then the config path is whatever you choose in your compose.yaml.
Frigate also has a built in config editor, so as long as you have it up and running with the correct storage path you can edit the configuration on the front end.
TBH, the phrase “skipped the docker” is a bit confusing. Running in LXC doesn’t mean you are not using docker, the script installs docker on the container. I personally don’t run it in a container, passing through storage and detector hardware can be challenging. Just spin up a small Debian VM, install docker and compose, and follow the frigate documentation. It’s very well written, and almost every problem you would run into is covered. It will give you the basics of the inner workings, and makes it much easier to pass through hardware and storage.
With one low res camera I ran it in a Debian vm with 4gb of Ram and two cores no problem. Once I had three 4K streams, I bumped it up to 16gb and 10 cores, only cause I wanted a hi-res live view, but I’m sure it would do fine with less with low res live view. Have been running it in a vm for two years now, no issues. Tried a bare metal install and lxc. Keep coming back to vm for the adaptability. Adding GPU and npu through lxc always made issues for me, but passing through to a vm is pretty well supported and documented, I think the ease of use outweighs the additional resources used by the vm. Plus I have read it’s not best practice to run docker inside an lxc.