Nowhere can I find documented WHICH 14 pins on the SparkFun Thing Plus - STM32 are the pins that support PWM output.
I’m probably wrong but there are 14 digital pins and the rest are analog capable. I’d venture to guess anything without a analog label is what you’re looking for.
I don’t have one to try but it should be pretty easy to whip up a sketch to test this.
Happy hacking!