There’s no consensus on anything on the internet, especially not in cycling training 
The Polarized training advocates generally say keep your easy days really easy, so more like mid Z2 of 7.
Inigo San Millan says just below LT1, which some people simplify to be roughly top of Z2 of 7. However, he’s notorious for not precisely defining things and stating it different ways, so his advice is really hard to pin down. And I say advice because he really doesn’t define a full training plan. Just some vague guidelines.
Polarized training is a bit more defined by some, like Seiler.