10 mins/km z2 pace

I have been running regularly since 2024, when I finished my first half marathon in 2.16 minutes, and for six months I ran 50-60 km weekly without a device. After getting a watch, what I thought was easy was actually upper zone 3 , did a VO2 max test and I got to know that my zone 2 pace is 10 minutes/ km. I was aerobic deficient. Two years down the line, there is still no difference. I just can’t achieve 80-20 every week. My weekly k is 52 minutes, 21.1k - 2.05 minutes. I am planning a 3.40-3.30 marathon in January. What can I do to achieve this goal? How can I become an efficient runner with a faster Z2 pace? I have no history of heart issues, ECG, blood work, and treadmill tests are normal. My sleep is 5-5.30 hrs with never getting 20% of REM and deep sleep in one night. I am 185 cm, 75 kg, in my mid 30s.