The interbreeding/unable to interbreed distinction isn’t all that relevant any more. There are far too many cases of hybridization between species, including some widely divergent. An extreme example of this is with American Paddlefish and Russian Sturgeon that have been separated for 184 million years, yet can still hybridize.
The current summary when it comes to species definitions is basically, “Well, it’s complicated.” As a result there are a number of different classifications schemes being used, not all of which include reproductive isolation as the primary distinguishing marker.
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A brief overview of 26 different ways to define a species - not paywalled
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Zachos 2016 An Annotated List of Species Concepts - paywalled