I run Channels-DVR on an LXC running Ubuntu with Proxmox. The container currently is sitting on one of my Proxmox hosts that is a Corei5 8th gen NUC. The only time I find the CPU usage is high is when commercial detection is running but it doesnt matter really if that takes 5min per recording instead of 2min.
I have also run the same LXC container on a Proxmox host with an AMD 5500GT and the only difference I noticed was the faster commercial detection.
I don't use transcoding myself as I just watch my recorded content back at its original quality but I tested my Nvidia 1060 and after setting Channels-DVR to use Nvec encoding tick box, I was able to use transcoding faster than I could watch the stream.
Personally I just find Channels-DVR works great in both Linux and in a container. Although LXC's can be different to Docker type containers in some areas.
Actually it must be popular to run the same setup I have as there is a Proxmox Community Script that automatically sets it all up for you someone has already made:
https://community-scripts.github.io/ProxmoxVE/scripts?id=channels&category=Media+%26+Streaming