Will the L9823 work at 3.3v with Wemos boards? Or is it 5v only?
https://www.st.com/en/automotive-analog-and-power/l9823.html
I see in the data sheet it lists under Absolute Maximum, Supply Voltage:  VDD -0.3v to 7v
Then, under Electrical Characteristics:  4.5 V &lt; VDD &lt; 5.5 V; unless otherwise specified.
Is the Electrical Characteristics section just listing values for an example voltage of 5v, or does the chip need 5v to work properly?
No. The undervoltage puts it in reset at 3.95V per the ST data sheet. It is a  5v only part with a wide tolerance on VCC. It was designed many years ago as an automotive part. It is a very nice part and performs well.