LXCs are more an alternative to VMs if your use-case supports it.
Docker is its own thing with pre-made application images.
VMs barely use more resources than LXC, debian minimal probably needs another 50MB of RAM in a VM vs LXC and that's about the only difference. It matters at scale but for home use it really doesn't IMO.
That said LXC has some benefits over a VM of being able to pass through mounts and parts of devices, those can be useful for Frigate where you want to use Intel Quicksync or OpenVINO and still share it with the host and other containers, because you can't do that on a VM unless you have a device you can dedicate to the VM only. You can also bind mount a directory on the host to a directory inside the container which is useful for sharing files between multiple containers.
It can be really frustrating to fix a bug, especially one caused by a huge change like switching to KDE because so many things have changed and could be the cause. Especially if you're not someone who likes to do that kind of stuff (me), and would prefer things just work in the first place so re-installing a KDE version is the way to go.