Alain, please confirm the speakers ARE working with macOS? You post suggests you are booting UB from an external drive, AND that your bluetooth speakers are working. I’m pretty sure there is an audio jack for earphones on the 2017 model - does the earphone jack have audio? I know this article linked sounds like magic thinking, but I did experience speakers working, then not. Your frustration is very real. I tried this:
I know it sounds stupid/simplistic when you read it, but after three tries… I know you certainly wouldn’t want to man-handle your iMac, but my last successful attempt was during an argument with a family member > POP! < Then all of a sudden the speakers were working. All of your current software solutions seems to have come to no avail. My suggestions are to:
• Boot back into macOS and determine if the speakers are working first (software vs hardware)
• Boot into Ubuntu Budgie and search for additional drivers. I always have to go back after the fact for the wifi drivers (like on my macbook). Perhaps it’s the same for newer speakers?
• Lie the iMac down face first and blow some canned air into the audio/ear phone jack. Have a good look with a magnifying glass and a flashlight. Is there hair/goop/shmutz in the port that might be confusing the audio jack? Do you have pets? Your post says:
alsamixer showing the correct card/unmuted
pulseaudio showing ati/hdmi off and internal card on in audio stereo duplex/output-unmuted
volume bars moving with media playing in chromium and firefox as well as VLC
which suggests to me that there is a physical reason you are muted
• Try that stupid sounding hardware solution last. It could very well be you have minutely shifted the audio jack just far enough away from the case, or some other internal physical thing that we can’t visually inspect because the iMac is a closed box.
Is this the 2017 with or without the new T2 security chip?
Anyways, your bluetooth connection seems to have audio consistently: that proves your bluetooth connection is successfully installed/working - A success! Please report back: my intent is to eventually replace the macOS on my current 2011 iMac once all this world crisis is over, and any final solutions you experience may be personally helpful to me