FYI/UPDATE : For future browsers who may purchase and use this, or a similar, screen on their Pi.
https://www.amazon.com/dp/B07S82CN57 - Longruner Raspberry Pi Touch Screen
It turns out the driver for the LCD set the GPU RAM to 64MB upon installation. I tried it on 2 other 3B+ units I had running RetroPie because it was bugging me, and it did the same on both of them.
Just to confirm, I set it back to 128, reinstalled the driver, and it went back to 64 each time.
So if you use this screen, or maybe one similar to it, check your GPU RAM allocation after you install the drivers, it may have changed. Especially if you move the Pi back to a higher resolution display.
Edit: To be more specific, running "sudo ./LCD-hdmi" will set it to 64 every time. In my case, and probably others, if you move back to a "standard" HDMI display and do not run this, you will not have audio at all, no matter what you set in the Raspberry Pi/RetroPie. So if you use this or any similar LCD, and you notice you lost audio when moving to something else, don't forget to run this. Then check your GPU RAM allocation.
:)