Measuring and Improving Serial Performance / Serial.flush() Blocks Forever on Nano 33 BLE Sense

@UKHeliBob
I don't understand why these two topics were merged, if you would read both of them you would see that one is describing a bug which I didn't know how to fix, and the other is asking why my measured data speeds are so slow.

Please consider undoing the merge as where I intend to take this discussion will appear to be off-topic to future readers.

Also have a good day (: