Will bulletproof coffee block my autophagy?

If you make bulletproof coffee with small amounts of additives, like 1 tablespoon of mct oil, 1 tablespoon of butter, this should be fine. It may inhibit the autophagy for a little bit, but it will kick back in shortly after.

Now, if you do half-and-half it may cause more difficulty due to some content of carbs and protein.

Autophagy is a state when you are in fasting mode and the body starts repairing and recycling its damaged proteins and microbes; in that state the need for vitamins and nutrients goes way down.