It used to be that I could export Opus inside MKV containers with various video formats.
Now if I switch audio to Opus, and video isn't VP8/VP9, there are no available containers I can output in, and Premiere Pro crashes if I click OK with no Muxers selected.
My Premiere Pro is fully updated, as is my Voukoder Linker and Voukoder.
I'm assuming this is easily reproducible, but I have no idea. Just try to encode a video with x265 and switch the audio codec to Opus, then check which Muxers are available. Also make sure the video's audio is set to 48khz in Premiere to avoid a different "bug". (Not really a bug, Opus needs 48khz)