Currently, FFmpeg libraries in Avidemux core fail to compile when built against the latest NVIDIA Video SDK headers (nv-codec-headers) as shipped e.g. by Fedora. As a workaround, please downgrade to 12.0.xx.x or 11.x.xx.x for now.
Build failure fixed (https://github.com/mean00/avidemux2/commit/5b637ae04773b417c9e6b47ba015abf458a9c151), unpinning the topic.