Several years ago there was a landslide on US89 that blocked the climb north of the US89alt turn off. While that was being repaired (over a year if I recall correctly), the Navajo route through Lechee was paved and made available as a detour (instead of the much longer detour via 98).
Google "chooses" routes more on time (that is distance * estimated speed), not on quality. So yes, if this is shorter, and it applies the same estimated speed, it will recommend it. That doesn't mean you should follow that.
From the streetview at the Sinclar gas station at the south end, people are still using this 'detour'. But there is a "watch for animals" sign right away - that is free range cattle. That's probably more of a concern if driving it at night.
Google has multiple years of streetview images for 89, but only part of IR 20 (from 2019). IR20 is clearly a lesser route, with narrower shoulders.
2013 item about paving N20. I forgot that it was that long ago!
https://azdot.gov/adot-blog/state-transportation-board-approves-funding-shorter-us-89-detourhttps://azdot.gov/node/8417