I absolutely could not figure this out anywhere online and many other people who tried to help were unable to solve the problem, so I reluctantly ended up dialoguing for perhaps 2-4 hours with ChatGPT, which actually managed to solve it. I'm not proud of doing so, but I'm not a programmer, either, and I really don't think the solution exists anywhere online after having searched and searched, which is why I'm documenting it here for anyone's future discovery.

Normally, when you install Mint on an iMac A2116, the local sound is silent, even though its sounds can be heard through remote desktop software. This is the way:

First-time setup:

sudo apt update
sudo apt install build-essential git linux-headers-$(uname -r)
cd ~
wget https://github.com/davidjo/snd_hda_macbookpro/archive/refs/heads/master.zip
unzip master.zip

Then the following steps should be done right after the commands above, as well as after every kernel update (which continually causes it to go silent again):

cd snd_hda_macbookpro-master
sudo ./install.cirrus.driver.sh

Then reboot and it'll work.

Trying to automate these bottom two lines into DKMS with:

cd ~/snd_hda_macbookpro-master
sudo ./install.cirrus.driver.sh --install

... seems to cause Mint to think its kernel management has gone corrupt, so I may try to make it a startup command via bash, though I welcome any ideas and thoughts about this process, which has worked so far on 22.2 and 22.3 'Zena.'