IgorBeg, in Preferences/Settings/Playback A what is the audio set to? The default on a new startup seems to be Alsa, default, 16 bit linear. Unfortunately I have no speakers on my Ubuntu 16 O/S, but when I download this new AppImage and load a ffmpeg 7.0 audio filter on my laptop, it works for me. I am confused by your bad results. Also, even though you get those error messages, are you getting audio because you say it is "scratchy", so it is working?
AppImage for my old UbuntuStudio.
Same messages and issues as before for me by my tests.
CLI output:
FFStream::encode_frame: encode failed.
file: /home/charlie/Documents/temp/pippo_ffmpeg7_test-20240421-2.webm
err: Resource temporarily unavailable
FFMPEG::mux_audio err: Operation not permitted
And the audio of the rendered file is full of scratches, unfortunately.