If you want to convert the episode to VP9/libvpx with ffmpeg:

ffmpeg -i "The.Pitt.S01E05.mkv" -c:v libvpx-vp9 -b:v 1M -c:a libopus output.webm Just reply with more detail — format, goal, and any error messages you have.

I notice you're asking about a feature related to and libvpx — but these two things don't normally go together.