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Many sources (including the Polar App) indicate Zone 2 is 60-70% of Max and Zone 3 is 70-80% of Max
If Im 40 (180 MHR) my MAF would be about 140 + or - adjustments
Zone 3 126-144
Zone 2 108-126
Ah, OK... Yeah, I think that may be reasonable, and for general trainees it's probably a good target. But I suspect if you go with the zone 2 training as described in the Peter Attia podcast, it would be a little higher than your Polar indicates. It also depends somewhat on the activity. Cycling, rowing, running, all may be a little different in really targeted zone 2 training for a trained endurance athlete.
Interested in @offwidth 's thoughts here...