how to confirm that PCB Ethernet layout does not affect perfornace
There could be no two "opinions" on this or that approach. Ethernet industry has long and successful history and developed standard techniques to evaluate-certify quality of communication channel. To start, read this application note from Agilent/Keysight on how to perform testing and interpret results. Or download Tektronix instructions.

And no, "Windows PC" has no means to generate test patterns, you need a special certified equipment for this.