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

Yeah, the fix is already merged in and will be in the next release. It sounds like that will be soon to come:
https://github.com/arduino/ArduinoCore-mbed/issues/357#issuecomment-958987118

facchinm commented 9 days ago

The plan was re-releasing this week but we are waiting a bit more to merge some more goodies, so next week the change will likely be live

Until then, it is necessary to manually apply the fix if you are using the release version that is available via Boards Manager.