The radio must use a stable voltage for power supply. The voltage of your solar panel is not constant and is pretty much a constant current source, so it cannot be used directly.
If you want to use it, you need to use a power conversion module to convert it to a constant voltage output.
The short circuit current is only about 1 mA, which is definitely not enough. Remember that the voltage is already zero at this point, what else can be provided?
To be honest, the calculator's solar panel is too small. You'd better buy one with an area of more than 6 square centimeters