I confirm that your advice is working. To do this, we need any terminal program that supports DTR monitoring. After turning on the DTR-monitoring, YUART via USB begin to be displayed. Of course, this is a bug and needs to be fixed.
Or in loop() you can use SerialUSB.dtr(true) then there is no need for a special program.
I noticed one oddity. If you do not use SerialUSB.dtr(true) or SerialUSB.dtr(false) in the code, then the data is displayed in the Arduino COM port monitor, and if, after starting it, you run it in a regular terminal that does not support DTR control, then in this terminal the data are displayed. But if, immediately after uploading the code, you run it in a regular terminal that does not support DRT, then the COM port data is not displayed.