SoftwareSerial will take over the entire Arduino board and many libraries will no longer work. Sending and receiving at the same time is a problem.
The Nano Every connects to the computer via Serial over usb [ADDED] (using a SAMD chip).
Then there is also a spare hardware Serial1 port at pin 0 and 1. You could do your test with Serial1, and then it should work.
If you really want a third Serial port, try AltSoftSerial. It functions in a different way, sometimes better, sometimes worse, but mostly better.
I don't know if AltSoftSerial is compatible with the Nano Every.