I just want to let people who helped me know that I got the project to work. I still need to attach a 2032 battery and figure out how to best trigger so it doesn't display continuously. Looking into sleep mode which seems promising.
The Tiny4kOLED library works well for this 64x32 screen. I decided to forgo the AHT20 library and instead access the sensor directly. The AHT sends its data in 5 bytes, 2 1/2 for humidity and 2 1/2 for temp. I don't understand why; 2 bytes each would be plenty of precision. Separating the halves was a challenge for me as I needed to learn about bit shifting and bitwise ands.
The final(?) sketch uses about 5k memory and the RAM demand
is apparently OK.
Thanks again to all of you generous folks who offered suggestions.