It is much more frequent than one would think.

In another life, I lost countless hours looking for complex solutions to problems with simple solutions.
eg: bad/cheap cables, dirty contacts, apparently compatible hardware, etc.

I learned long ago to always check the basics first.

Is this with the same hardware?
ie: same laptop, same cable, same external monitor

Does the monitor have two ports ie: VGA and HDMI?

A monitor I use (Dell P1914S) does, it detects which port is being accessed and flashes it on the screen* when I switch on the box and before the system is up.
* after the cable has been disconnected and reconnected, even if the monitor is not connected to mains. 

Let's see: please boot your laptop without the HDMI cable / monitor connected and then run this in a terminal:

~$ xrandr

And then repeat the operation after rebooting with the HDMI cable / monitor connected.

Please post the terminal printout of each.

Edit:

With the monitor not connected you should see something akin to this ...

~$ xrandr
Screen 0: minimum 320 x 200, current 1024 x 600,
maximum 4096 x 4096
LVDS1 connected primary 1024x600+0+0 (normal left inverted right x axis y axis) 220mm x 129mm
1024x600      60.00*+  65.00
1024x576      59.90    59.82
--- snip ---
VGA1 disconnected (normal left inverted right x axis y axis)
~$

... and with the monitor connected something akin to this ...

~$ xrandr
Screen 0: minimum 320 x 200, current 1024 x 600, maximum 4096 x 4096 
LVDS1 connected primary 1024x600+0+0 (normal left inverted right x axis y axis) 220mm x 129mm
1024x600      60.00*+  65.00
1024x576      59.90    59.82
--- snip ---
VGA1 connected (normal left inverted right x axis y axis)  # <- external VGA monitor on
1024x768      60.00 +  75.03    70.07                           VGA port of a netbook
832x624       74.55
--- snip ---
~$

Best,

A.

Although I noticed that the monitor has a VGA port... I'm not sure if it'll make any difference but might as well try that, too.

Have you tried using another cable or that same cable/external display combination with another source.
ie: not your laptop.

Best,

A.

How to Install and Configure PipeWire in Linux

And then running PipeWire manually just to test things out:

https://github.com/MX-Linux/pipewire-se … wire-start

Unfortunately, this didn't work either and it even took away the audio from the laptop speakers and now only headphones work. Not that I actually care all that much since the laptop speakers are not very good anyway, but just to document what's going on.

Please, any help on this is much appreciated. Thank you.

I'm having some issues with audio that I haven't been able to figure out. My setup is a laptop and an external monitor, which has built-in speakers, connected via HDMI. When I open the Audio Mixer, I can see there is a profile created for it but it says unavailable as you can see in the screenshot:

Selecting that option, or any of the other HDMI options, results in not audio playing at all. Selecting Analog Stereo Output works normally but it plays the audio from the laptop. With this option, I can also play audio from my headphones normally, so it's really just the external display that is not working properly, as far as audio is concerned.

I thought this might have been because of the non-free firmware since Debian 12 handled this out of the box, but upon checking /etc/apt/sources.list the repositories are set to download from it.