More information; looks like something broke with newer Raspian releases. I went back to Raspian 8 (Jesse) and the first thing I noticed was the dmesg output is different:
ttyS0 at MMIO 0x0 (irq=220, base_baud=31250000) is a 16550
If I recall, with Raspian 11, the base_baud was 50000000
I’m happy knowing the hardware is OK, but what is my path forward with newer Raspian releases?