This is an old bug on some Linux builds and desktop environments. I do not know why. We simply make a high level call in Qt, and then it is largely out of our hands. Perhaps a future upgrade to Qt will make a difference. For me, on Ubuntu 20.04 with GNOME Shell, it works in Flatpak and AppImage as well as my local compile. There is probably a file missing in our portable and snap, but I do not know.
can the proxy format be chosen ? I have an H/W compatible encoder, and it can perform HEVC or X264 … but I’m not sure enabled means “selected”. I see the proxy are in HEVC
Covered in the docs (below), but turn off hardware encoder for x264.