I use an Asus E510 laptop. After upgrading from Ubuntu 22.04 to Ubuntu 24.04 the left audio channel is now shared across both speakers on the output device (my TV) and the right channel audio signal is not sent.
Clean booting into Ubuntu 24.04 or Ubuntu 26.04 from a live disk also causes the problem, so it is not a problem caused by a damaged or jumbled upgrade. Clean booting back into Ubuntu 22.04 from a live disk fixes the problem again, so it is not a setting on my TV nor is there anything wrong with my laptop or HDMI cable. I have also tested with multiple HDMI cables to be sure.
There are also issues with the new 5.1 and 7.1 HDMI output modes in Ubuntu 24.04 and onward where the right side channels do not respond appropriately.
This is an untenable situation.